libc: Add missing fdatasync() implementation

Change-Id: I04bb655d77e414021e1f2a973329167ad76ca1c4
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 4bcccb5..baac5d0 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -118,6 +118,7 @@
 int         ftruncate(int, off_t)  93
 int         getdents:getdents64(unsigned int, struct dirent *, unsigned int)   217,220
 int         fsync(int)  118
+int         fdatasync(int) 148
 int         fchown:fchown32(int, uid_t, gid_t)  207
 void        sync(void)  36
 int         __fcntl64:fcntl64(int, int, void *)  221