[Support] fix mingw-w64 build

[lh123]

Summary

Mingw-w64 does not define _beginthreadex_proc_type, so we should replace it with unsigned (__stdcall *ThreadFunc)(void *).
fix https://github.com/clangd/clangd/issues/188

[mstorsjo]

FWIW, the latest git version of mingw-w64 has this typedef (since llvm started using it here a couple weeks ago), but being able to compile with older versions might be good of course,

[lh123]

In D69879#1735009, @mstorsjo wrote:

FWIW, the latest git version of mingw-w64 has this typedef (since llvm started using it here a couple weeks ago), but being able to compile with older versions might be good of course,

Yes, introduced by rGa9c3c176ad74

[ilya-biryukov]

LGTM

[lh123]

In D69879#1735061, @ilya-biryukov wrote:

LGTM

I don't have commit access, can you commit it for me?

llvm/lib/Support/Windows/Threading.inc

 
 static unsigned __stdcall threadFuncAsync(void *Arg) {
   std::unique_ptr<AsyncThreadInfo> Info(static_cast<AsyncThreadInfo *>(Arg));
   (*Info)();
   return 0;
 }
 
 static void
-llvm_execute_on_thread_impl(_beginthreadex_proc_type ThreadFunc, void *Arg,
+llvm_execute_on_thread_impl(unsigned (__stdcall *ThreadFunc)(void *), void *Arg,
                             llvm::Optional<unsigned> StackSizeInBytes,
                             JoiningPolicy JP) {
   HANDLE hThread = (HANDLE)::_beginthreadex(
       NULL, StackSizeInBytes.getValueOr(0), ThreadFunc, Arg, 0, NULL);
 
   if (!hThread) {
     ReportLastErrorFatal("_beginthreadex failed");
   }