This patch consolidates Linux sync_file_range at default
sysdeps/unix/sysv/linux/sync_file_range.c implementation. It also
moves the rules flags from generic io/Makefile to Linux one due the
fact it is a Linux-only symbol.
Checked on i686-linux-gnu and x86_64-linux-gnu.
* io/Makefile (CFLAGS-sync_file_range.c): Remove rule.
* sysdeps/unix/sysv/linux/Makefile (CFLAGS-sync_file_range.c): New
rule.
* sysdeps/unix/sysv/linux/wordsize-64/syscalls.list: Remove
sync_file_range.