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.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@180084 138bc75d-0d04-0410-961f-82ee72b054a4