build: statically link MinGW runtime in LLVM tools on Windows

Signed-off-by: deadprogram <ron@hybridgroup.com>

.github/workflows/windows.yml

@@ -65,7 +65,7 @@ jobs:
         uses: actions/cache/restore@v5
         id: cache-llvm-build
         with:
-          key: llvm-build-20-windows-v4
+          key: llvm-build-20-windows-v5
           path: llvm-build
       - name: Build LLVM
         if: steps.cache-llvm-build.outputs.cache-hit != 'true'

GNUmakefile

@@ -142,6 +142,9 @@ ifeq ($(OS),Windows_NT)
 
     # PIC needs to be disabled for libclang to work.
     LLVM_OPTION += -DLLVM_ENABLE_PIC=OFF
+    # Statically link the C++ and GCC runtime into LLVM tools so they don't
+    # depend on MinGW DLLs that may not be on PATH when executed during the build.
+    LLVM_OPTION += '-DCMAKE_EXE_LINKER_FLAGS=-static-libgcc -static-libstdc++'
 
     CGO_CPPFLAGS += -DCINDEX_NO_EXPORTS
     CGO_LDFLAGS += -static -static-libgcc -static-libstdc++