Fix compilation error when using clang-cl 16 or higher

Fixes a "Incompatible function pointer types" error.

In prior versions, this was a warning, but is now an error.

CLA: trivial

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from #20654)

crypto/thread/arch/thread_win.c

@@ -13,7 +13,7 @@
 # include <process.h>
 # include <windows.h>
 
-static DWORD __stdcall thread_start_thunk(LPVOID vthread)
+static unsigned __stdcall thread_start_thunk(LPVOID vthread)
 {
     CRYPTO_THREAD *thread;
     CRYPTO_THREAD_RETVAL ret;