Mesa build system fixes

[Jon M. Taylor]

        I just comitted a bunch of fixes to the Mesa autoconf/automake
system, and everything appears to be building properly again.  Well, I
haven't tracked down that libMesaGGI.la incompatibility yet, but other
than that....

Jon

---
'Cloning and the reprogramming of DNA is the first serious step in 
becoming one with God.'
        - Scientist G. Richard Seed