Update the Makefiles and includes for the new paths.
Note that there hasn't been no separation of the Makefiles yet, and make is
jumping all over the place. That will be taken care shortly. But for now, make
should work. It was tested with linux and linux-dri. Linux-cell and linux-llvm
might require some minor tweaks.
Most of the programs list their dependencies on the Mesa libraries in
their Makefiles. This works with the default configuration where
APP_LIB_DEPS only lists external libraries. This changes the
linux-osmesa configs and the osdemos Makefile to follow that convention.
Some cleanup of the Makefile is also added to refer to the GL libraries
through the existing variables rather than hardcoding their names.