mesa/es: Improve Makefile rules.

Make sure glapi headers are cleaned when "make clean".  Make sure all
sources depend on subdirs-stamp-tmp so that sources/headers are
generated first.

subdirs-stamp-tmp will be removed after a successful build.  It might be
a problem when a build fails.  But it is much better than where we
currently are: glapi headers are never cleaned or re-generated.
2 files changed