win32: thread: use the proper signature for DllMain

_DECL_DLLMAIN is needed to get the signature of DllMain. But depending
whether windows.h is included the signature differs (WINAPI, HANDLE, etc).
This is only the case in mingw-w64. In the Windows SDK there's only the
definition without the fancy types.

We need to include process.h before windows.h so we have the same definition
as the Windows SDK.

src/win32/thread.c

@@ -30,6 +30,7 @@
 #endif
 
 #define _DECL_DLLMAIN
+#include <process.h>
 #include <vlc_common.h>
 #include <vlc_threads.h>
 #include <vlc_charset.h>
@@ -706,7 +707,7 @@ void vlc_threads_setup(libvlc_int_t *vlc)
 
 #define LOOKUP(s) (((s##_) = (void *)GetProcAddress(h, #s)) != NULL)
 
-BOOL WINAPI DllMain (HANDLE hinstDll, DWORD fdwReason, LPVOID lpvReserved)
+int __stdcall DllMain (void *hinstDll, unsigned fdwReason, void *lpvReserved)
 {
     (void) hinstDll;
     (void) lpvReserved;