fix dummied-out fsync

if we eventually have build options, it might be nice to make an
option to dummy this out again, in case anybody needs a system-wide
disable for disk/ssd-thrashing, etc. that some daemons do when
logging...

src/unistd/fsync.c

@@ -3,6 +3,5 @@
 
 int fsync(int fd)
 {
-	//return syscall(SYS_fsync, fd);
-	return 0;
+	return syscall(SYS_fsync, fd);
 }