win32/pthread: avoid name clashes with winpthread

The mingw-w64 GCC seems to link implicitly to libwinpthread, which does
implement a pthread emulation (that is more complete than Git's). Let's
keep preferring Git's.

To avoid linker errors where it thinks that the `pthread_self` and the
`pthread_create` symbols are defined twice, let's give our version a
`win32_` prefix, just like we already do for `pthread_join()`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

compat/win32/pthread.c

@@ -21,8 +21,8 @@ static unsigned __stdcall win32_start_routine(void *arg)
 	return 0;
 }
 
-int pthread_create(pthread_t *thread, const void *unused,
-		   void *(*start_routine)(void *), void *arg)
+int win32_pthread_create(pthread_t *thread, const void *unused,
+			 void *(*start_routine)(void *), void *arg)
 {
 	thread->arg = arg;
 	thread->start_routine = start_routine;
@@ -53,7 +53,7 @@ int win32_pthread_join(pthread_t *thread, void **value_ptr)
 	}
 }
 
-pthread_t pthread_self(void)
+pthread_t win32_pthread_self(void)
 {
 	pthread_t t = { NULL };
 	t.tid = GetCurrentThreadId();

compat/win32/pthread.h

@@ -50,8 +50,9 @@ typedef struct {
 	DWORD tid;
 } pthread_t;
 
-int pthread_create(pthread_t *thread, const void *unused,
-		   void *(*start_routine)(void*), void *arg);
+int win32_pthread_create(pthread_t *thread, const void *unused,
+			 void *(*start_routine)(void*), void *arg);
+#define pthread_create win32_pthread_create
 
 /*
  * To avoid the need of copying a struct, we use small macro wrapper to pass
@@ -62,7 +63,8 @@ int pthread_create(pthread_t *thread, const void *unused,
 int win32_pthread_join(pthread_t *thread, void **value_ptr);
 
 #define pthread_equal(t1, t2) ((t1).tid == (t2).tid)
-pthread_t pthread_self(void);
+pthread_t win32_pthread_self(void);
+#define pthread_self win32_pthread_self
 
 static inline void NORETURN pthread_exit(void *ret)
 {