conformtest: Add mips XFAIL for struct stat st_dev type (bug 17786).

As noted in bug 17786, MIPS o32 struct stat has the wrong type of
st_dev.  This patch XFAILs that test in the conformtest expectations
for this case (the test still fails after the patch because there's
also a similar issue for st_rdev that needs reporting and XFAILing
separately, and the bug should not be closed without an actual fix,
not just XFAILing).

Tested for mips with build-many-glibcs.py.

	[BZ #17786]
	* sysdeps/unix/sysv/linux/mips/mips32/Makefile: New file.
	* conform/data/sys/stat.h-data (stat.st_dev): XFAIL for
	mips-o32-linux.