libXmu-devel 0.99.1-2 seems to be missing a lot of other -devel dependencies, see the pkgconfig file and #includes in installed headers.
Thanks for the report. The pkg config files in modular X are all broken right now, and specify a bunch of things that they should not. This is currently being fixed in upstream CVS by Kevin Martin. I'll leave this open to track the issue for now, until we decide wether we're going to wait for X11R7 RC3, or apply patches from CVS.
Thanks, with RC3's fixed pkgconfig files, I've barebonesed the deps, and did a rebuild with a bare system, only installing listed deps. Needed to add pkgconfig and libXau-devel, and now she builds cleanly. Fixed in libXmu-0.99.2-1