github: Compile i686 libcxx tests with an x86_64 build of the compiler

Some tests in the libcxx testsuite require more than 2 GB of memory
to compile currently.

Author: mstorsjo

.github/workflows/build.yml

@@ -338,9 +338,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        arch:
-          - x86_64
-          - i686
+        include:
+          - { arch: x86_64, prefix: i686-w64-mingw32- }
+          - { arch: x86_64, prefix: }
     steps:
       - name: Install dependencies
         run: |
@@ -374,8 +374,8 @@ jobs:
             -DLIBCXX_ENABLE_WERROR=YES `
             -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" `
             -DLIBCXX_CXX_ABI=libcxxabi `
-            -DCMAKE_C_COMPILER=clang `
-            -DCMAKE_CXX_COMPILER=clang++ `
+            -DCMAKE_C_COMPILER=${{matrix.prefix}}clang `
+            -DCMAKE_CXX_COMPILER=${{matrix.prefix}}clang++ `
             -DLIBCXXABI_ENABLE_SHARED=NO `
             -DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=YES `
             -DLIBCXX_USE_COMPILER_RT=YES `

.github/workflows/test-libcxx.yml

@@ -44,9 +44,9 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        arch:
-          - x86_64
-          - i686
+        include:
+          - { arch: x86_64, prefix: i686-w64-mingw32- }
+          - { arch: x86_64, prefix: }
     steps:
       - name: Install dependencies
         run: |
@@ -86,8 +86,8 @@ jobs:
             -DLIBCXX_ENABLE_WERROR=YES `
             -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" `
             -DLIBCXX_CXX_ABI=libcxxabi `
-            -DCMAKE_C_COMPILER=clang `
-            -DCMAKE_CXX_COMPILER=clang++ `
+            -DCMAKE_C_COMPILER=${{matrix.prefix}}clang `
+            -DCMAKE_CXX_COMPILER=${{matrix.prefix}}clang++ `
             -DLIBCXXABI_ENABLE_SHARED=NO `
             -DLIBCXX_ENABLE_STATIC_ABI_LIBRARY=YES `
             -DLIBCXX_USE_COMPILER_RT=YES `