This moves the compatibility include files from include to
include/compat so we can use the awful MS C compiler
<../include/> trick to emulate the GNU #include_next extension.
This also removes a few old compat files we do not need anymore.
Move define adjustments to CPPFLAGS.
Adjust user CFLAGS directly, do not override during configuration.
USER_CFLAGS is not necessary to build libcompat_noopt correctly.
This makes building and testing easier because the library Makefile.am
files are use directly rather than as templates. Thanks to Wouter Clarie
for the idea.
