Optimize pthread_cond_init

Use __builtin_memset to init pthread_cond_t.

Issue: #I7M851
Test: libctest, benchmark
Signed-off-by: Nlitao <litao@kaihong.com>
Change-Id: Ib30428b82df4eebe7788f88e2638189e5afa1f97

musl_src.gni

@@ -2125,6 +2125,7 @@ musl_src_porting_file = [
   "src/thread/pthread_cond_timedwait_monotonic_np.c",
   "src/thread/pthread_cond_timeout_np.c",
   "src/thread/pthread_cond_clockwait.c",
+  "src/thread/pthread_cond_init.c",
   "src/thread/pthread_create.c",
   "src/thread/pthread_rwlock_clockwrlock.c",
   "src/thread/pthread_rwlock_timedwrlock_monotonic_np.c",

porting/linux/user/src/thread/pthread_cond_init.c

+#include "pthread_impl.h"
+
+int pthread_cond_init(pthread_cond_t *restrict c, const pthread_condattr_t *restrict a)
+{
+	__builtin_memset(c, 0, sizeof(pthread_cond_t));
+	if (a) {
+		c->_c_clock = a->__attr & 0x7fffffff;
+		if (a->__attr>>31) c->_c_shared = (void *)-1;
+	}
+	return 0;
+}