Rollup merge of rust-lang#50644 - kennytm:read-appveyor-dump, r=alexc…

…richton

AppVeyor: Read back trace from crash dump on failure.

This is an attempt to debug spurious access violations on Windows (rust-lang#33434, rust-lang#50604). Thanks to rust-lang#50276, there should be minidumps to read when rustc segfault.

(The implementation is based on <https://github.com/springmeyer/travis-coredump/blob/master/test.bat>.)

appveyor.yml

@@ -211,6 +211,11 @@ test_script:
   - set NO_CCACHE=1
   - sh src/ci/run.sh
 
+on_failure:
+  # Dump crash log
+  - set PATH=%PATH%;"C:\Program Files (x86)\Windows Kits\10\Debuggers\X64"
+  - if exist %LOCALAPPDATA%\CrashDumps for %%f in (%LOCALAPPDATA%\CrashDumps\*) do cdb -c "k;q" -G -z "%%f"
+
 branches:
   only:
     - auto