xfsprogs: don't include all xfs headers just for crc32

xfsprogs: don't include all xfs headers just for crc32

Brian Norris reported that "The $BUILD_CC toolchain might have an
older set of Linux headers than the $CC toolchain. It's generally
unsafe to try to build both with the same definitions, but in
particular, this one can cause compilation failures in the local
crc32selftest build: [failure to find fsmap.h]"

It seems like the most straightforward thing to do here is include
a specific set of system headers, instead of pulling in the whole
xfs.h header chain which has multiple tests and definitions in
place for headers that may or may not be there during the build.

Reported-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Tested-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>