llvm: Disable pthreads on mingw-w64 platforms

configure

@@ -878,6 +878,13 @@ do
         # Try to have LLVM pull in as few dependencies as possible (#9397)
         LLVM_OPTS="$LLVM_OPTS --disable-zlib --disable-libffi"
 
+        # pthreads works badly on mingw-w64 systems: #8996
+        case "$CFG_BUILD" in
+            (*w64-mingw32)
+            LLVM_OPTS="$LLVM_OPTS --disable-pthreads"
+            ;;
+        esac
+
         case "$CFG_C_COMPILER" in
             ("ccache clang")
             LLVM_CXX_32="ccache clang++ -m32 -Qunused-arguments"