After an upgrade of my gentoo system, I got in some problems, first with compiling qt, and then with compiling the ati-drivers. After looking want might be wrong and looking for other with similar problems, I finally found out that some files in /usr/include/GL linked to non-existing files, in particular /usr/include/GL/gl.h.

Running eselect opengl set 2 (in my case for xorg-x11) fixed these non-existing links and my ati-drivers worked again!