don't omit setting errno in internal __map_file function

a caller needs the reason for open (or fstat, albeit unlikely) failure
if it's going to make decisions about continuing a path search or
similar.

src/time/__map_file.c

@@ -7,9 +7,9 @@ const char unsigned *__map_file(const char *pathname, size_t *size)
 {
 	struct stat st;
 	const unsigned char *map = MAP_FAILED;
-	int fd = __sys_open(pathname, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
+	int fd = sys_open(pathname, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
 	if (fd < 0) return 0;
-	if (!__syscall(SYS_fstat, fd, &st)) {
+	if (!syscall(SYS_fstat, fd, &st)) {
 		map = __mmap(0, st.st_size, PROT_READ, MAP_SHARED, fd, 0);
 		*size = st.st_size;
 	}