Trim superfluous PATH fiddling.

Now that the 'tesla' script does all of the requisite searching for TESLA binaries, drop all of this PATH funny business.
Demo: BUILD_DIR -> TESLA_BUILD_DIR.

TESLA_BUILD_DIR is an environment variable that might be set anyway.
Drop superfluous definition from CFLAGS.

The tesla.mk file sets '-D TESLA'; no need to do it in the main Makefile, too.
Pass all varargs to __tesla_struct_automaton.

We may be about to change the signature of __tesla_struct_automaton; it would be nice if we didn't have to run around changing tesla-macros.h too.
Reduce fragility with regex.

Don't look for exact line numbers in output strings; these things can be subject to change!
Centralise tesla-macros.h.

There's no need for four copies of the same tesla-macros.h file...
Trivial: whitespace.