autoconf: refactor ostype.m4

autoconf: refactor ostype.m4

Further refactoring of the autoconf macros. Move more linux and solaris
specific checks into their own files.

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/12843
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 3c2e39bab7d927aa5f20d02a5e327927a4b2b553)

Change-Id: I4d91753afd90e4735ab61413e757f6852750a3de
Reviewed-on: https://gerrit.openafs.org/12877
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>