Add cmake based build
Add cmake based build

This is meant for the release because users often expect things like an
install target pkg-config scripts or project files for their favorite
IDE.

Main firm development will stay with the simple Makefile, we only plan
to update the cmake build for releases.

libfirm/libfirm,libfirm/libfirm,jonashaag/libfirm,MatzeB/libfirm,MatzeB/libfirm,jonashaag/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,jonashaag/libfirm,jonashaag/libfirm,jonashaag/libfirm,MatzeB/libfirm,libfirm/libfirm,jonashaag/libfirm,jonashaag/libfirm,MatzeB/libfirm,libfirm/libfirm