test: Do a minimal test to try to build the libcxx std c++ module

.github/workflows/build.yml

@@ -85,6 +85,7 @@ jobs:
           # llvm-mingw).
           LLVM_CMAKEFLAGS="-DLLVM_ENABLE_LIBXML2=OFF -DLLVM_ENABLE_TERMINFO=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm-mingw --disable-clang-tools-extra
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
+          ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           RUN_I686=false RUN_X86_64=false ./run-tests.sh $(pwd)/install/llvm-mingw
           cd install
           DISTRO=ubuntu-$(grep DISTRIB_RELEASE /etc/lsb-release | cut -f 2 -d =)-$(uname -m)
@@ -129,6 +130,7 @@ jobs:
       - name: Test using the cross-built assembled toolchain
         run: |
           sudo apt-get update && sudo apt-get install qemu-user-static libc6-arm64-cross libstdc++6-arm64-cross
+          QEMU_LD_PREFIX=/usr/aarch64-linux-gnu ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           QEMU_LD_PREFIX=/usr/aarch64-linux-gnu RUN_I686=false RUN_X86_64=false ./run-tests.sh $(pwd)/install/llvm-mingw
       - name: Package the toolchain
         env:
@@ -206,6 +208,7 @@ jobs:
           # other (arm64) architecture form.
           MACOS_REDIST=1 LLVM_CMAKEFLAGS="-DLLVM_ENABLE_ZSTD=OFF -DLLDB_ENABLE_PYTHON=OFF" ./build-all.sh $(pwd)/install/llvm-mingw --disable-clang-tools-extra
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
+          ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           RUN_I686=false RUN_X86_64=false ./run-tests.sh $(pwd)/install/llvm-mingw
           cd install
           NAME=llvm-mingw-$TAG-ucrt-macos-universal
@@ -263,6 +266,7 @@ jobs:
           ./build-all.sh $(pwd)/install/llvm-mingw --disable-clang-tools-extra --disable-lldb $ARGS
           .github/workflows/store-version.sh install/llvm-mingw/versions.txt
           ./copy-msys-dependencies.sh $(pwd)/install/llvm-mingw ${{matrix.sys}}
+          ./test-libcxx-module.sh $(pwd)/install/llvm-mingw
           ./run-tests.sh $(pwd)/install/llvm-mingw
           cd install
           NAME=llvm-mingw-$TAG-ucrt-msys2-${{matrix.sys}}
@@ -358,6 +362,7 @@ jobs:
       - uses: actions/checkout@v4
       - name: Run tests
         run: |
+          ./test-libcxx-module.sh /llvm-mingw
           ./run-tests.sh /llvm-mingw
           ./run-lldb-tests.sh /llvm-mingw