build: Some minor improvements to appveyor

* Add cache support
* Finish all build jobs if one failed

Author: tesuji

appveyor.yml

@@ -12,16 +12,20 @@ cache:
   - target
 
 environment:
-  RUSTFLAGS: -Ctarget-feature=+crt-static
-  RUST_BACKTRACE: 1
+  global:
+    RUSTFLAGS: -Ctarget-feature=+crt-static
+    RUST_BACKTRACE: 1
   matrix:
-  - TARGET: x86_64-pc-windows-msvc
-    NO_ADD: 1
-    ALLOW_PR: 1
-  - TARGET: i686-pc-windows-msvc
+    - TARGET: x86_64-pc-windows-msvc
+      NO_ADD: 1
+      ALLOW_PR: 1
+    - TARGET: i686-pc-windows-msvc
   access_token:
     secure: q8Wqx0brgfpOYFQqWauvucE2h0o1WYb41a3gKaCKV9QiE4eTz6qLNlqyC3mdsp4Q
 
+matrix:
+  fast_finish: true     # set this flag to immediately finish build once one of the jobs fails.
+
 install:
   # If this is a PR and we're not allowed to test PRs, skip the whole build.
   # Also if we're on the master branch no need to run the full test suite, so