defining CALL_DUMMY_LOCATION as BEFORE_TEXT_END. This is
because machines that do this will also have to know to
set NEED_TEXT_START_END. Besides, it was a redundant way to
say the same thing.
* tm-29k.h, tm-convex.h, tm-np1.h: Eliminate
CANNOT_EXECUTE_STACK, define CALL_DUMMY_LOCATION and
NEED_TEXT_START_END.
Allow the register definitions to be overridden in another
tm-file. Fix SR_REGNUM. Add a mess of _REGNUM's. Separate
RETURN_REGNUM from GR96_REGNUM and DUMMY_SAVE_GREGS from
DUMMY_SAVE_GR96, for handling kernel calling conventions
that use GR64+ rather than GR96+.
