WIP: github: Skip cxxabi tests on arm64ec

cxxabi has a few expectedly failing tests on arm64ec:

  llvm-libc++abi-mingw.cfg.in :: forced_unwind1.pass.cpp
  llvm-libc++abi-mingw.cfg.in :: forced_unwind2.pass.cpp
  llvm-libc++abi-mingw.cfg.in :: forced_unwind3.pass.cpp

Additionally, the following tests are failing:

  llvm-libc++-mingw.cfg.in :: std/language.support/support.coroutines/coroutine.handle/coroutine.handle.noop/noop_coroutine.pass.cpp
  llvm-libc++-mingw.cfg.in :: std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array.pass.cpp
  llvm-libc++-mingw.cfg.in :: std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete.pass.cpp

The sized_delete ones can be fixed by adding recognition of arm64ec
as mingw target triple for a workaround in those tests.

The noop_coroutine.pass.cpp case is not analyzed yet.

Author: mstorsjo

.github/workflows/build.yml

@@ -429,7 +429,7 @@ jobs:
             -DCMAKE_INSTALL_MESSAGE=NEVER `
             -DLLVM_LIT_ARGS="-v --time-tests"
           ninja
-          ninja check-runtimes
+          ninja ${{(matrix.target_arch == 'arm64ec') && 'check-cxx check-unwind' || 'check-runtimes'}}
 
   # Run the OpenMP tests with the cross-built toolchains from above.
   # This also forces testing the bundled python executables.