grab bag of changes aimed at getting stack splitting to work:
- morestack support for 5l and arm runtime
- argsize support in 5c, 5l, ar and nm. assembly code from 5a
will break in interesting ways unless NOSPLIT is specified
- explicit cond execution constants
- fix 5l output to use %d instead of %ld so that negative
values show.
- added a lot of code to arm/asm.s. runtime entry code almost
working currently aborts at gogo not implemented