[CI: Make workaround for #3901 a bit less ugly]

Author: kinke

.github/actions/helper-build-ldc/action.yml

@@ -30,11 +30,14 @@ runs:
         installDir="$PWD/install"
         mkdir '${{ inputs.build_dir }}'
         cd '${{ inputs.build_dir }}'
+        # wrt. CMAKE_C[XX]_COMPILER for Apple: https://github.com/ldc-developers/ldc/issues/3901
         cmake -G Ninja ../ldc \
           -DCMAKE_BUILD_TYPE=Release \
           -DLLVM_ROOT_DIR="$PWD/../${{ inputs.llvm_dir }}" \
           -DD_COMPILER='${{ inputs.host_dc }}' \
           -DLDC_LINK_MANUALLY=OFF \
+          ${{ runner.os == 'macOS' && '-DCMAKE_C_COMPILER=/usr/bin/cc' || '' }} \
+          ${{ runner.os == 'macOS' && '-DCMAKE_CXX_COMPILER=/usr/bin/c++' || '' }} \
           ${{ inputs.specify_install_dir == 'true' && '-DCMAKE_INSTALL_PREFIX="$installDir"' || '' }} \
           ${{ inputs.specify_install_dir == 'true' && '-DINCLUDE_INSTALL_DIR="$installDir/import"' || '' }} \
           ${{ inputs.cmake_flags }}

.github/workflows/main.yml

@@ -39,18 +39,13 @@ jobs:
           - job_name: macOS x86_64
             os: macos-12
             arch: x86_64
-            # wrt. CMAKE_C[XX]_COMPILER: https://github.com/ldc-developers/ldc/issues/3901
             bootstrap_cmake_flags: >-
               -DBUILD_LTO_LIBS=ON
-              -DCMAKE_C_COMPILER=/usr/bin/cc
-              -DCMAKE_CXX_COMPILER=/usr/bin/c++
             # https://github.com/ldc-developers/ldc/issues/4462:
             # When using LTO, we need to explicitly export ~all symbols for plugin support via `ld64 -exported_symbol '__*'`.
             # Additionally `-w` to suppress resulting linker warnings.
             extra_cmake_flags: >-
               -DBUILD_LTO_LIBS=ON
-              -DCMAKE_C_COMPILER=/usr/bin/cc
-              -DCMAKE_CXX_COMPILER=/usr/bin/c++
               -DD_COMPILER_FLAGS="-O -flto=full -defaultlib=phobos2-ldc-lto,druntime-ldc-lto -L-exported_symbol '-L__*' -L-w"
               -DEXTRA_CXXFLAGS=-flto=full
             with_pgo: true
@@ -60,12 +55,8 @@ jobs:
             arch: arm64
             bootstrap_cmake_flags: >-
               -DBUILD_LTO_LIBS=ON
-              -DCMAKE_C_COMPILER=/usr/bin/cc
-              -DCMAKE_CXX_COMPILER=/usr/bin/c++
             extra_cmake_flags: >-
               -DBUILD_LTO_LIBS=ON
-              -DCMAKE_C_COMPILER=/usr/bin/cc
-              -DCMAKE_CXX_COMPILER=/usr/bin/c++
               -DD_COMPILER_FLAGS="-O -flto=full -defaultlib=phobos2-ldc-lto,druntime-ldc-lto -L-exported_symbol '-L__*' -L-w"
               -DEXTRA_CXXFLAGS=-flto=full
             with_pgo: true