debloat: use __syscall instead of syscall where possible

don't waste time (and significant code size due to function call
overhead!) setting errno when the result of a syscall does not matter
or when it can't fail.

src/stdio/__fdopen.c

@@ -20,8 +20,8 @@ FILE *__fdopen(int fd, const char *mode)
 
 	/* Set append mode on fd if opened for append */
 	if (*mode == 'a') {
-		int flags = syscall(SYS_fcntl, fd, F_GETFL, 0);
-		syscall(SYS_fcntl, fd, F_SETFL, flags | O_APPEND);
+		int flags = __syscall(SYS_fcntl, fd, F_GETFL);
+		__syscall(SYS_fcntl, fd, F_SETFL, flags | O_APPEND);
 	}
 
 	f->fd = fd;

src/stdio/__lockfile.c

@@ -15,6 +15,6 @@ void __lockfile(FILE *f)
 	}
 	while (a_cas(&f->lock, 0, tid))
 		if (spins) spins--, a_spin();
-		else syscall(SYS_sched_yield);
+		else __syscall(SYS_sched_yield);
 	f->lockcount = 1;
 }

src/stdio/fopen.c

@@ -27,7 +27,7 @@ FILE *fopen(const char *filename, const char *mode)
 	f = __fdopen(fd, mode);
 	if (f) return f;
 
-	syscall(SYS_close, fd);
+	__syscall(SYS_close, fd);
 	return 0;
 }
 

src/stdio/tmpfile.c

@@ -17,7 +17,7 @@ FILE *tmpfile(void)
 		fd = syscall(SYS_open, s, O_RDWR|O_CREAT|O_EXCL|O_LARGEFILE, 0600);
 		if (fd >= 0) {
 			f = __fdopen(fd, "w+");
-			syscall(SYS_unlink, s);
+			__syscall(SYS_unlink, s);
 			return f;
 		}
 	}

src/thread/pthread_mutex_trylock.c

@@ -14,7 +14,7 @@ int pthread_mutex_trylock(pthread_mutex_t *m)
 
 	if (m->_m_type >= 4) {
 		if (!self->robust_list.off)
-			syscall(SYS_set_robust_list,
+			__syscall(SYS_set_robust_list,
 				&self->robust_list, 3*sizeof(long));
 		self->robust_list.off = (char*)&m->_m_lock-(char *)&m->_m_next;
 		self->robust_list.pending = &m->_m_next;

src/thread/pthread_self.c

@@ -22,7 +22,7 @@ static int init_main_thread()
 	main_thread.errno_ptr = __errno_location();
 	libc.errno_location = errno_location;
 	main_thread.tid = main_thread.pid = 
-		syscall(SYS_set_tid_address, &main_thread.tid);
+		__syscall(SYS_set_tid_address, &main_thread.tid);
 	return 0;
 }
 

src/unistd/sync.c

@@ -3,5 +3,5 @@
 
 void sync(void)
 {
-	syscall(SYS_sync);
+	__syscall(SYS_sync);
 }