Shorten compile commands run by the build system

Shorten compile commands run by the build system

The DEFS line in MCONFIG had gotten so long that it exceeded 4k, and
this was starting to cause some tools heartburn.  It also made "make
V=1" almost useless, since trying to following the individual commands
run by make was lost in the noise of all of the defines.

So fix this by putting the configure-generated defines in lib/config.h
and the directory pathnames to lib/dirpaths.h.

In addition, clean up some vestigal defines in configure.in and in the
Makefiles to further shorten the cc command lines.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>