Build doxymacs HEAD, and fix to build with clang

Doxymacs doesn't build with clang.  I have fixed this, though I don't know if my patch is acceptable since I used `inreplace` instead of a proper patch.  I couldn't get the patch at [netbsd patch](http://ftp.netbsd.org/pub/pkgsrc/current/pkgsrc/devel/doxymacs/patches/patch-c_doxymacs__parser.c) to work correctly from within homebrew.

Additionally, I added the ability to build off of HEAD which has a half dozen commits after the 1.8.0 release, including support for `//!` style C++ comments.