use __fstat instead of __fstatat with AT_EMPTY_PATH in __map_file

this isolates knowledge of the nonstandard AT_EMPTY_PATH extension to
one place and returns __map_file to its prior simplicity.

src/time/__map_file.c

@@ -1,4 +1,3 @@
-#define _BSD_SOURCE
 #include <sys/mman.h>
 #include <fcntl.h>
 #include <sys/stat.h>
@@ -10,7 +9,7 @@ const char unsigned *__map_file(const char *pathname, size_t *size)
 	const unsigned char *map = MAP_FAILED;
 	int fd = sys_open(pathname, O_RDONLY|O_CLOEXEC|O_NONBLOCK);
 	if (fd < 0) return 0;
-	if (!__fstatat(fd, "", &st, AT_EMPTY_PATH)) {
+	if (!__fstat(fd, &st)) {
 		map = __mmap(0, st.st_size, PROT_READ, MAP_SHARED, fd, 0);
 		*size = st.st_size;
 	}