linux: Consolidate sync_file_range implementation

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.