autoconf: refactor acinclude.m4

autoconf: refactor acinclude.m4

The acinclude.m4 is very large and often requires to be changed for
unrelated commits.  Divy up the large acinclude.m4 into a number of
smaller files to avoid so many contentions and to make the autoconf
system easier to maintain.

This is a non-functional change. Care has been taken preserve the
ordering of the autoconf tests. Except for whitespace, the generated
configure file has not been changed by this refactoring.  This has been
verified with a 'diff -u -w -B' comparison of the generated configure
file before and after applying this commit.

Reviewed-on: https://gerrit.openafs.org/12842
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit c72622a244e561173e86ffe88ee3c9a8c823a76a)

Change-Id: I9504eaa2430fd35f79b55c3df96c82cc7e58fafd
Reviewed-on: https://gerrit.openafs.org/12876
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>