winpthreads: Add missing `__stdcall` on lazy-binding function pointers

Signed-off-by: LIU Hao <lh_mouse@126.com>

mingw-w64-libraries/winpthreads/src/thread.c

diff --git a/mingw-w64-libraries/winpthreads/src/thread.c b/mingw-w64-libraries/winpthreads/src/thread.c
index 36ee665..3fc5ced 100644
--- a/mingw-w64-libraries/winpthreads/src/thread.c
+++ b/mingw-w64-libraries/winpthreads/src/thread.c
@@ -75,8 +75,8 @@
   return EXCEPTION_CONTINUE_SEARCH;
 }
 
-static PVOID (*AddVectoredExceptionHandlerFuncPtr) (ULONG, PVECTORED_EXCEPTION_HANDLER);
-static ULONG (*RemoveVectoredExceptionHandlerFuncPtr) (PVOID);
+static PVOID (WINAPI *AddVectoredExceptionHandlerFuncPtr) (ULONG, PVECTORED_EXCEPTION_HANDLER);
+static ULONG (WINAPI *RemoveVectoredExceptionHandlerFuncPtr) (PVOID);
 
 static void __attribute__((constructor))
 ctor (void)