Support -fdebug-cpp option

Support -fdebug-cpp option

This patch adds -fdebug-cpp option. When used with -E this dumps the
relevant macro map before every single token. This clutters the output
a lot but has proved to be invaluable in tracking some bugs during the
development of the virtual location support.

Co-Authored-By: Dodji Seketeli <dodji@redhat.com>
From-SVN: r180084