Fix posix_spawn getrlimit64 namespace (bug 17991).

Fix posix_spawn getrlimit64 namespace (bug 17991).

posix_spawn (a standard POSIX function) brings in a use of getrlimit64
(not a standard POSIX function).  This patch fixes this by using
__getrlimit64 and making getrlimit64 a weak alias.

This is more complicated than some such changes because of files that
define getrlimit64 in their own way using symbol versioning after
including the main sysdeps/unix/sysv/linux/getrlimit64.c with a
getrlimit macro defined.  There are various existing patterns for such
cases in glibc; the one I've used here is that a getrlimit64 macro
disables the weak_alias / libc_hidden_weak calls, leaving it to the
including file to define the getrlimit64 name in whatever way is
appropriate.

Tested for x86_64 and x86 that installed stripped shared libraries are
unchanged by this patch.

	[BZ #17991]
	* include/sys/resource.h (__getrlimit64): Declare.  Use
	libc_hidden_proto.
	* resource/getrlimit64.c (getrlimit64): Rename to __getrlimit64
	and define as weak alias of __getrlimit64.  Use libc_hidden_weak.
	* sysdeps/posix/spawni.c (__spawni): Call __getrlimit64 instead of
	getrlimit64.
	* sysdeps/unix/sysv/linux/getrlimit64.c (getrlimit64): Rename to
	__getrlimit64.
	[!getrlimit64] (getrlimit64): Define as weak alias of
	__getrlimit64.  Use libc_hidden_weak.
	* sysdeps/unix/sysv/linux/i386/getrlimit64.c (getrlimit64): Define
	using __getrlimit64 not __new_getrlimit64.
	(__GI_getrlimit64): Likewise.
	* sysdeps/unix/sysv/linux/mips/getrlimit64.c (getrlimit64):
	Likewise.
	(__GI_getrlimit64): Likewise.
	(__old_getrlimit64): Use __getrlimit64 not __new_getrlimit64.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/syscalls.list
	(getrlimit): Add __getrlimit64 alias.
	* sysdeps/unix/sysv/linux/wordsize-64/syscalls.list (getrlimit):
	Likewise.
	* conform/Makefile (test-xfail-XOPEN2K/spawn.h/linknamespace):
	Remove variable.
	(test-xfail-POSIX2008/spawn.h/linknamespace): Likewise.
	(test-xfail-XOPEN2K8/spawn.h/linknamespace): Likewise.