conformtest: XFAIL tv_nsec tests for x32 (bug 16437).

This patch XFAILs the conformtest tv_nsec tests for x32 so that the
incorrect type does not potentially hide other failures.  As this is
not a fix for the bug, it should remain open in Bugzilla.

Tested (compilation only) with build-many-glibcs.py.

	[BZ #16437]
	* sysdeps/unix/sysv/linux/x86_64/x32/Makefile
	[$(subdir) = conform] (conformtest-xfail-conds): New variable.
	* conform/data/signal.h-data (timespec.tv_nsec): XFAIL for
	x86_64-x32-linux.
	* conform/data/sys/select.h-data (timespec.tv_nsec): Likewise.
	* conform/data/sys/stat.h-data (timespec.tv_nsec): Likewise.
	* conform/data/time.h-data (timespec.tv_nsec): Likewise.