We probably should get rid of assert() entirely, but at this stage it is
more useful for things to crash where we can catch it in a debugger.
With compile_error() we have a single place to set an error flag (to
bail out and return an error on the next instruction) so that will be a
small change later when enough of the compiler bugs are sorted.

But re-arrange/cleanup the error/assert stuff so we at least get a dump
of the TGSI that triggered it.  So we see some useful output in piglit
logs.

Signed-off-by: Rob Clark <robclark@freedesktop.org>