Don't build PKINIT ASN.1 support code if not building PKINIT plugin

Don't build PKINIT ASN.1 support code if not building PKINIT plugin

If --disable-pkinit is given at configure time, don't build the PKINIT
plugin.

If the PKINIT plugin is not going to be built, define DISABLE_PKINIT.

If DISABLE_PKINIT is defined, don't build the PKINIT-related ASN.1
encoding and decoding routines, and fill their slots in the accessor
function table with null pointers.

Tweak the accessor table initialization to use conditionally-varying
macros rather than conditionally selecting between two blocks of
invocations of fixed macros.

ticket: new

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@20652 dc483132-0cff-0310-8789-dd5450dbe970