Add Linux 4.13 constants to bits/fcntl-linux.h.

This patch adds new interfaces (F_GET_RW_HINT etc., and associated
RW[FH]_WRITE_LIFE_*) from Linux 4.13 to bits/fcntl-linux.h
(conditional on __USE_GNU).

Tested for x86_64.

	* sysdeps/unix/sysv/linux/bits/fcntl-linux.h [__USE_GNU]
	(F_GET_RW_HINT): New macro.
	[__USE_GNU] (F_SET_RW_HINT): Likewise.
	[__USE_GNU] (F_GET_FILE_RW_HINT): Likewise.
	[__USE_GNU] (F_SET_FILE_RW_HINT): Likewise.
	[__USE_GNU] (RWF_WRITE_LIFE_NOT_SET): Likewise.
	[__USE_GNU] (RWH_WRITE_LIFE_NONE): Likewise.
	[__USE_GNU] (RWH_WRITE_LIFE_SHORT): Likewise.
	[__USE_GNU] (RWH_WRITE_LIFE_MEDIUM): Likewise.
	[__USE_GNU] (RWH_WRITE_LIFE_LONG): Likewise.
	[__USE_GNU] (RWH_WRITE_LIFE_EXTREME): Likewise.