Add MADV_WIPEONFORK, MADV_KEEPONFORK from Linux 4.14.

This patch adds the new MADV_WIPEONFORK and MADV_KEEPONFORK from Linux
4.14 to bits/mman-linux.h (and bits/mman.h in the hppa case).  Note
there are further hppa MADV_* changes in 4.14; I plan a separate glibc
patch for those.

Tested for x86_64.

	* sysdeps/unix/sysv/linux/bits/mman-linux.h
	[__USE_MISC] (MADV_WIPEONFORK): New macro.
	[__USE_MISC] (MADV_KEEPONFORK): Likewise.
	* sysdeps/unix/sysv/linux/hppa/bits/mman.h
	[__USE_MISC] (MADV_WIPEONFORK): Likewise.
	[__USE_MISC] (MADV_KEEPONFORK): Likewise.