Userspace libxfs is supposed to match the kernel libxfs except for the
preprocessor include directives. Fix a few discrepancies that came up
for whatever reason.
To fix the build errors resulting from CONFIG_XFS_RT not being defined,
add it to libxfs.h and alter the Makefile to track xfs_rtbitmap.h.
Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Bill O'Donnell <bodonnel@redhat.com>