Auto merge of #58575 - mati865:musl_toolchain, r=<try>

WIP Musl host toolchain

Based on #55163 and #57359
Depends on #55566

CC #57439

### How it works

Tested compiler made by `dist` on glibc and musl based distributions and verified binaries it produces:
* Ubuntu (glibc) - installed it as a target for host toolchain and observed no regressions for static (default) linking, dynamic linking apparently requires musl build libgcc so I didn't test it.
* Alpine (musl) - installed as the host toolchain, by default it links statically (executables are portable and work on glibc distributions) but with `-C target-feature=-crt-static` Rust flag it links dynamically (executables require musl built libraries).

### What's debatable

It should be decided whether this toolchain should link dynamically or statically when using it on musl distribution. I believe the distributions would prefer dynamic linking but it'd be misleading because `$ARCH-unknown-linux-musl` target links statically on the other hosts.
Another problem is using `RUSTFLAGS='-C target-feature=-crt-static'` for dynamic builds which is really uncomfortable.

To address both issues I suggest leaving `$ARCH-unknown-linux-musl` static for both host and cross target and introducing "alias triple" `$ARCH-unknown-linux-dynmusl`. It'd be the same as `$ARCH-unknown-linux-musl` (and use the same libraries to avoid duplication) but it'd link dynamically.

<del>
### Why it's still WIP (help wanted)

I'm having a hard time getting all tests to pass and I'd appreciate help.

Non-verbose error:
<details>

```
Testing proc_macro stage1 (x86_64-unknown-linux-musl -> x86_64-unknown-linux-musl)
   Compiling proc_macro v0.0.0 (/checkout/src/libproc_macro)
error[E0463]: can't find crate for `std`

error[E0463]: can't find crate for `std`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
[RUSTC-TIMING] proc_macro test:true 0.529
[RUSTC-TIMING] proc_macro test:false 0.530
error: Could not compile `proc_macro`.
warning: build failed, waiting for other jobs to finish...
error: Could not compile `proc_macro`.

To learn more, run the command again with --verbose.

command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-musl" "-j" "16" "--release" "--locked" "--manifest-path" "/checkout/src/libtest/Cargo.toml" "-p" "proc_macro" "--"
expected success, got: exit code: 101

failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test --host x86_64-unknown-linux-musl --target x86_64-unknown-linux-musl
```
</details>

Verbose error:
<details>

```
Testing proc_macro stage1 (x86_64-unknown-linux-musl -> x86_64-unknown-linux-musl)
   Compiling proc_macro v0.0.0 (/checkout/src/libproc_macro)
     Running `/checkout/obj/build/bootstrap/debug/rustc --edition=2018 --crate-name proc_macro src/libproc_macro/lib.rs --color never --crate-type lib --emit=dep-info,link -C opt-level=2 -C metadata=09ddd3ecc930ab63 -C extra-filename=-09ddd3ecc930ab63 --out-dir /checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps --target x86_64-unknown-linux-musl -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/release/deps -C target-feature=-crt-static`
     Running `/checkout/obj/build/bootstrap/debug/rustc --edition=2018 --crate-name proc_macro src/libproc_macro/lib.rs --color never --emit=dep-info,link -C opt-level=2 --test -C metadata=a564d363930469c8 -C extra-filename=-a564d363930469c8 --out-dir /checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps --target x86_64-unknown-linux-musl -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/release/deps -C target-feature=-crt-static`
error[E0463]: can't find crate for `std`
error[E0463]: can't find crate for `std`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
error: aborting due to previous error

For more information about this error, try `rustc --explain E0463`.
[RUSTC-TIMING] proc_macro test:false 0.248
error: Could not compile `proc_macro`.

Caused by:
  process didn't exit successfully: `/checkout/obj/build/bootstrap/debug/rustc --edition=2018 --crate-name proc_macro src/libproc_macro/lib.rs --color never --crate-type lib --emit=dep-info,link -C opt-level=2 -C metadata=09ddd3ecc930ab63 -C extra-filename=-09ddd3ecc930ab63 --out-dir /checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps --target x86_64-unknown-linux-musl -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/release/deps -C target-feature=-crt-static` (exit code: 1)
warning: build failed, waiting for other jobs to finish...
[RUSTC-TIMING] proc_macro test:true 0.248
error: Could not compile `proc_macro`.

Caused by:
  process didn't exit successfully: `/checkout/obj/build/bootstrap/debug/rustc --edition=2018 --crate-name proc_macro src/libproc_macro/lib.rs --color never --emit=dep-info,link -C opt-level=2 --test -C metadata=a564d363930469c8 -C extra-filename=-a564d363930469c8 --out-dir /checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps --target x86_64-unknown-linux-musl -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps -L dependency=/checkout/obj/build/x86_64-unknown-linux-musl/stage1-test/release/deps -C target-feature=-crt-static` (exit code: 1)

command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-musl" "-j" "16" "--release" "--locked" "--manifest-path" "/checkout/src/libtest/Cargo.toml" "--verbose" "-p" "proc_macro" "--"
expected success, got: exit code: 101

failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test --host x86_64-unknown-linux-musl --target x86_64-unknown-linux-musl
```

</details>

Whole tests non-verbose output: [rust-tests.log](https://github.com/rust-lang/rust/files/2879945/rust-tests.log)

I think the error is because build system (correctly?) tries to use `obj/build/x86_64-unknown-linux-musl/stage1-test/x86_64-unknown-linux-musl/release/deps` which is empty but `obj/build/x86_64-unknown-linux-gnu/stage1-test/x86_64-unknown-linux-musl/release/deps` contains required libs.
</del>

Author: bors

.travis.yml

@@ -17,7 +17,7 @@ matrix:
   include:
     # Images used in testing PR and try-build should be run first.
     - env: IMAGE=x86_64-gnu-llvm-6.0 RUST_BACKTRACE=1
-      if: type = pull_request OR branch = auto
+      if: branch = auto
 
     - env: IMAGE=dist-x86_64-linux DEPLOY=1
       if: branch = try OR branch = auto
@@ -159,7 +159,7 @@ matrix:
     - env: IMAGE=dist-x86_64-freebsd DEPLOY=1
       if: branch = auto
     - env: IMAGE=dist-x86_64-musl DEPLOY=1
-      if: branch = auto
+#      if: branch = auto
     - env: IMAGE=dist-x86_64-netbsd DEPLOY=1
       if: branch = auto
     - env: IMAGE=asmjs
@@ -185,7 +185,7 @@ matrix:
     - env: IMAGE=x86_64-gnu-distcheck
       if: branch = auto
     - env: IMAGE=mingw-check
-      if: type = pull_request OR branch = auto
+      if: branch = auto
 
     - stage: publish toolstate
       if: branch = master AND type = push

src/ci/docker/dist-x86_64-musl/Dockerfile

@@ -4,6 +4,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
   g++ \
   make \
   file \
+  wget \
   curl \
   ca-certificates \
   python2.7 \
@@ -18,19 +19,17 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 WORKDIR /build/
 
-COPY scripts/musl.sh /build/
+COPY scripts/musl-toolchain.sh /build/
 # We need to mitigate rust-lang/rust#34978 when compiling musl itself as well
-RUN CC=gcc \
-    CFLAGS="-Wa,-mrelax-relocations=no" \
-    CXX=g++ \
-    CXXFLAGS="-Wa,-mrelax-relocations=no" \
-    bash musl.sh x86_64 && rm -rf /build
+# TODO: Check what this issue is and if we can ignore it
+
+RUN bash musl-toolchain.sh x86_64-linux-musl && rm -rf build
 
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
 ENV RUST_CONFIGURE_ARGS \
-      --musl-root-x86_64=/musl-x86_64 \
+      --musl-root-x86_64=/usr/local/x86_64-linux-musl \
       --enable-extended \
       --disable-docs
 
@@ -41,6 +40,15 @@ ENV RUST_CONFIGURE_ARGS \
 # See: https://github.com/rust-lang/rust/issues/34978
 ENV CFLAGS_x86_64_unknown_linux_musl=-Wa,-mrelax-relocations=no
 
+ENV HOSTS=x86_64-unknown-linux-musl \
+    CC_x86_64_unknown_linux_musl=x86_64-linux-musl-gcc \
+    CXX_x86_64_unknown_linux_musl=x86_64-linux-musl-g++
+
+#    CARGO_TARGET_ARM_UNKNOWN_LINUX_MUSLEABIHF_LINKER=musl-gcc \
+#    CARGO_TARGET_ARM_UNKNOWN_LINUX_MUSLEABIHF_RUNNER="qemu-arm -L /musl-arm"
+
+ENV RUSTFLAGS="-C target-feature=-crt-static"
+
 ENV SCRIPT \
-      python2.7 ../x.py test --target x86_64-unknown-linux-musl && \
-      python2.7 ../x.py dist --target x86_64-unknown-linux-musl
+      python2.7 ../x.py test --target $HOSTS && \
+      python2.7 ../x.py dist --host $HOSTS --target $HOSTS

src/ci/docker/scripts/musl-toolchain.sh

@@ -0,0 +1,66 @@
+set -ex
+
+hide_output() {
+  set +x
+  on_err="
+echo ERROR: An error was encountered with the build.
+cat /tmp/build.log
+exit 1
+"
+  trap "$on_err" ERR
+  bash -c "while true; do sleep 30; echo \$(date) - building ...; done" &
+  PING_LOOP_PID=$!
+  $@ &> /tmp/build.log
+  trap - ERR
+  kill $PING_LOOP_PID
+  rm /tmp/build.log
+  set -x
+}
+
+TARGET=$1
+#ARCH=$1
+#TARGET=linux-musl-$ARCH
+ARCH=x86_64
+
+OUTPUT=/usr/local
+shift
+
+git clone https://github.com/richfelker/musl-cross-make -b v0.9.7
+cd musl-cross-make
+
+hide_output make -j$(nproc) TARGET=$TARGET
+hide_output make install TARGET=$TARGET OUTPUT=$OUTPUT
+
+cd -
+
+# Make musl binaries executable
+
+ln -s $OUTPUT/$TARGET/lib/libc.so /lib/ld-musl-$ARCH.so.1
+echo $OUTPUT/$TARGET/lib >> /etc/ld-musl-$ARCH.path
+
+
+export CC=$TARGET-gcc
+export CXX=$TARGET-g++
+
+LLVM=70
+
+# may have been downloaded in a previous run
+if [ ! -d libunwind-release_$LLVM ]; then
+  curl -L https://github.com/llvm-mirror/llvm/archive/release_$LLVM.tar.gz | tar xzf -
+  curl -L https://github.com/llvm-mirror/libunwind/archive/release_$LLVM.tar.gz | tar xzf -
+fi
+
+mkdir libunwind-build
+cd libunwind-build
+cmake ../libunwind-release_$LLVM \
+          -DLLVM_PATH=/build/llvm-release_$LLVM \
+          -DLIBUNWIND_ENABLE_SHARED=0 \
+          -DCMAKE_C_COMPILER=$CC \
+          -DCMAKE_CXX_COMPILER=$CXX \
+          -DCMAKE_C_FLAGS="$CFLAGS" \
+          -DCMAKE_CXX_FLAGS="$CXXFLAGS"
+
+hide_output make -j$(nproc)
+cp lib/libunwind.a $OUTPUT/$TARGET/lib
+cd - && rm -rf libunwind-build
+