xfstests: a few fixes to Makefile

xfstests: a few fixes to Makefile

Change the top-level Makefile, to make it clearer just what makes
what, and what depends on what:
- Separate the rules for "configure" and "include/builddefs" into
  two parts, each of which generate one of the files
- Get rid of the rule for include/config.h, and group it with the
  one for include/builddefs (the same command creates both files)

Having done this, we find that having both "include/builddefs" and
"include/config.h" as dependencies for the default target results in
a parallel invocation of "make" spawning two concurrent attempts to
do the configure step--and that doesn't work.

Creating one of those two will result in the other getting created,
so just list one of them as a dependency for the default rule.

A couple of other small fixes:
- Get rid of the "new", "remake" and "check" dependencies for the
  default rule, which serv no purpose
- Use the $(Q) convention in a few missed spots
- Stop a DMAPI-only comment from getting echoed on default build
- Delete the "

This updated version pulls in the content of a patch previously
posted separately to fix the problem with parallel builds.

Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Eric Sandeen <sandeen@sandeen.net>