xfstests: Use common rules to build binaries

xfstests: Use common rules to build binaries

Remove explicit target-per-file rules in the subdirectories being
built and replace them with target based rules using the buildrules
hooks for doing this.  This results in the makefiles being simpler,
smaller and more consistent. It does mean that all binaries are
linked against the common set of libraries but this does not cause
any harm.

This patch does not address the dmapi subdirectory of the xfstests
build system.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>