Fix wordsize-64 posix_fadvise64, posix_fallocate64 namespace (bug 17777).

Fix wordsize-64 posix_fadvise64, posix_fallocate64 namespace (bug 17777).

On systems using sysdeps/unix/sysv/linux/wordsize-64, posix_fadvise64
and posix_fallocate64 (non-POSIX) are strong aliases for posix_fadvise
and posix_fallocate (POSIX), meaning references to the latter wrongly
bring in definitions of the former.  They should be weak aliases; this
patch makes them so.

Tested for x86_64 (testsuite, and that disassembly of installed shared
libraries is unchanged by the patch).

	[BZ #17777]
	* sysdeps/unix/sysv/linux/wordsize-64/posix_fadvise.c
	(posix_fadvise64): Define as weak alias not strong alias.
	* sysdeps/unix/sysv/linux/wordsize-64/posix_fallocate.c
	(posix_fallocate64): Likewise.
	* conform/Makefile (test-xfail-XOPEN2K/fcntl.h/linknamespace):
	Remove variable.
	(test-xfail-XOPEN2K/mqueue.h/linknamespace): Likewise.
	(test-xfail-POSIX2008/fcntl.h/linknamespace): Likewise.
	(test-xfail-POSIX2008/mqueue.h/linknamespace): Likewise.
	(test-xfail-XOPEN2K8/fcntl.h/linknamespace): Likewise.
	(test-xfail-XOPEN2K8/mqueue.h/linknamespace): Likewise.