Allow older LLVM versions to have missing components

This check was introduced by #77280 to ensure that all tests that are
filtered by LLVM component are actually tested in CI. However this
causes issues for new targets (e.g. #101069) where support is only
available on the latest LLVM version.

This PR restricts the tests to only CI jobs that use the latest LLVM
version.

Author: Amanieu

src/ci/docker/host-x86_64/x86_64-gnu-llvm-14-stage1/Dockerfile

@@ -32,6 +32,10 @@ RUN sh /scripts/sccache.sh
 # LLVM, rather than the typical src/llvm-project LLVM.
 ENV NO_DOWNLOAD_CI_LLVM 1
 
+# This is not the latest LLVM version, so some components required by tests may
+# be missing.
+ENV IS_NOT_LATEST_LLVM 1
+
 # Using llvm-link-shared due to libffi issues -- see #34486
 ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \

src/ci/docker/host-x86_64/x86_64-gnu-llvm-14/Dockerfile

@@ -38,6 +38,10 @@ RUN sh /scripts/sccache.sh
 # LLVM, rather than the typical src/llvm-project LLVM.
 ENV NO_DOWNLOAD_CI_LLVM 1
 
+# This is not the latest LLVM version, so some components required by tests may
+# be missing.
+ENV IS_NOT_LATEST_LLVM 1
+
 # Using llvm-link-shared due to libffi issues -- see #34486
 ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \

src/ci/docker/host-x86_64/x86_64-gnu-llvm-15/Dockerfile

@@ -40,6 +40,10 @@ RUN sh /scripts/sccache.sh
 # LLVM, rather than the typical src/llvm-project LLVM.
 ENV NO_DOWNLOAD_CI_LLVM 1
 
+# This is not the latest LLVM version, so some components required by tests may
+# be missing.
+ENV IS_NOT_LATEST_LLVM 1
+
 # Using llvm-link-shared due to libffi issues -- see #34486
 ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \

src/ci/run.sh

@@ -138,7 +138,11 @@ if [ "$RUST_RELEASE_CHANNEL" = "nightly" ] || [ "$DIST_REQUIRE_ALL_TOOLS" = "" ]
     RUST_CONFIGURE_ARGS="$RUST_CONFIGURE_ARGS --enable-missing-tools"
 fi
 
-export COMPILETEST_NEEDS_ALL_LLVM_COMPONENTS=1
+# Unless we're using an older version of LLVM, check that all LLVM components
+# used by tests are available.
+if [ "$IS_NOT_LATEST_LLVM" = "" ]; then
+  export COMPILETEST_NEEDS_ALL_LLVM_COMPONENTS=1
+fi
 
 # Print the date from the local machine and the date from an external source to
 # check for clock drifts. An HTTP URL is used instead of HTTPS since on Azure