Tweak configure script generation to check that all symbols produced

Tweak configure script generation to check that all symbols produced
via AC_DEFINE are also present in the applicable configure-generated
header file, and error out otherwise.  Currently doesn't apply in appl
and test trees.

* util/check-ac-syms: New script.
* config/post.in (.acsyms_okay): New target; runs check-ac-syms, unless we're
in the appl or tests trees.
(configure): Depend on .acsyms_okay.
* config/pre.in (AUTOCONF_HEADER): New variable.
* plugins/kdb/db2/libdb2/Makefile.in (AUTOCONF_HEADER): New variable.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@17955 dc483132-0cff-0310-8789-dd5450dbe970