github: Include libcxxabi and libunwind tests in the test-libcxx job too

These test suites now pass in the latest git main.

This target isn't run automatically anywhere, but in case the
target is enabled to run the tests, include the libcxxabi and libunwind
test suites too.

.github/workflows/build.yml

@@ -281,6 +281,8 @@ jobs:
     # testing with the latest compiler instead of an older release).
     # Therefore, keep the test disabled by default; it's easy to enable
     # temporarily on a branch for testing.
+    # The libcxxabi and libunwind tests don't pass on the pinned 16.x branch,
+    # only on git main.
     if: false
     needs: [linux-cross]
     runs-on: windows-latest
@@ -332,7 +334,7 @@ jobs:
             -DLIBCXXABI_USE_LLVM_UNWINDER=YES `
             -DLIBCXX_EXTRA_SITE_DEFINES="__USE_MINGW_ANSI_STDIO=1;TEST_IS_EXECUTED_IN_A_SLOW_ENVIRONMENT"
           ninja
-          ninja check-cxx
+          ninja check-cxx check-cxxabi check-unwind
 
   # Run the OpenMP tests with the cross-built i686/x86_64 toolchains from above.
   # This also forces testing the bundled python executables.