fdatasync: handle latest alpha syscalls

The latest alpha Linux kernel defines __NR_fdatasync like everyone else and
deprecates the older __NR_osf_fdatasync, so support that setup.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

libc/sysdeps/linux/common/fdatasync.c

@@ -10,7 +10,7 @@
 #include <sys/syscall.h>
 #include <unistd.h>
 
-#if defined __NR_osf_fdatasync
+#if !defined __NR_fdatasync && defined __NR_osf_fdatasync
 # define __NR_fdatasync __NR_osf_fdatasync
 #endif