Added build.info debugging capability to Configure

This is only enabled when the environment variable
CONFIGURE_DEBUG_BUILDINFO is defined.  This will cause every line in
every build.info file to be displayed, along with the content of the
skip stack before and after parsing.  This can be a very powerful tool
to see that all conditions are working as expected.

Reviewed-by: Rich Salz <rsalz@openssl.org>