mingw: uglify (a, 0) definitions to shut up warnings

When the result of a (a, 0) expression is not used, MSys2's GCC version
finds it necessary to complain with a warning:

	right-hand operand of comma expression has no effect

Let's just pretend to use the 0 value and have a peaceful and quiet life
again.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/nedmalloc/malloc.c.h

@@ -1802,9 +1802,10 @@ struct win32_mlock_t
   volatile long threadid;
 };
 
+static inline int return_0(int i) { return 0; }
 #define MLOCK_T               struct win32_mlock_t
 #define CURRENT_THREAD        win32_getcurrentthreadid()
-#define INITIAL_LOCK(sl)      (memset(sl, 0, sizeof(MLOCK_T)), 0)
+#define INITIAL_LOCK(sl)      (memset(sl, 0, sizeof(MLOCK_T)), return_0(0))
 #define ACQUIRE_LOCK(sl)      win32_acquire_lock(sl)
 #define RELEASE_LOCK(sl)      win32_release_lock(sl)
 #define TRY_LOCK(sl)          win32_try_lock(sl)

compat/win32/pthread.h

@@ -18,7 +18,10 @@
  */
 #define pthread_mutex_t CRITICAL_SECTION
 
-#define pthread_mutex_init(a,b) (InitializeCriticalSection((a)), 0)
+static inline int return_0(int i) {
+	return 0;
+}
+#define pthread_mutex_init(a,b) return_0((InitializeCriticalSection((a)), 0))
 #define pthread_mutex_destroy(a) DeleteCriticalSection((a))
 #define pthread_mutex_lock EnterCriticalSection
 #define pthread_mutex_unlock LeaveCriticalSection