Suppress warnings on mingw

This trivial patch fixes the following warnings on mingw.

----
pthread-win32.c:20: warning: no previous prototype for 'pthread_self'
dllwrap --def pgevent.def -o pgevent.dll pgevent.o pgmsgevent.o
Warning: resolving _DllUnregisterServer by linking to _DllUnregisterServer(at)0
Use --enable-stdcall-fixup to disable these warnings
Use --disable-stdcall-fixup to disable these fixups
Warning: resolving _DllRegisterServer by linking to _DllRegisterServer(at)0
Warning: resolving _DllUnregisterServer by linking to _DllUnregisterServer(at)0
Use --enable-stdcall-fixup to disable these warnings
Use --disable-stdcall-fixup to disable these fixups
Warning: resolving _DllRegisterServer by linking to _DllRegisterServer(at)0
----

Index: src/bin/pgevent/pgevent.def
===================================================================
--- src/bin/pgevent/pgevent.def (HEAD)
+++ src/bin/pgevent/pgevent.def (working copy)
@@ -1,4 +1,4 @@
; dlltool --output-def pgevent.def pgevent.o pgmsgevent.o
EXPORTS
- DllUnregisterServer ;
- DllRegisterServer ;
+ DllUnregisterServer = DllUnregisterServer(at)0 ;
+ DllRegisterServer = DllRegisterServer(at)0 ;
Index: src/port/pthread-win32.h
===================================================================
--- src/port/pthread-win32.h (HEAD)
+++ src/port/pthread-win32.h (working copy)
@@ -5,7 +5,7 @@
typedef HANDLE pthread_mutex_t;
typedef int pthread_once_t;

-DWORD pthread_self();
+DWORD pthread_self(void);

void pthread_setspecific(pthread_key_t, void *);
void *pthread_getspecific(pthread_key_t);

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center