o Fix _longjmp() to return 1 when the return value is given as 0.

o  Fix _longjmp() to return 1 when the return value is given as 0.
o  Remove the unwanted smartness in _longjmp() where it compares
   the current ar.bspstore with the saved ar.bspstore and restores
   ar.rnat based on it. This either avoids saving ar.rnat in the
   jmp_buf or is the consequence of not saving ar.rnat. All this
   complexity breaks libc_r where we use longjmp() to switch to
   different threads and the current ar.bspstore has no relation
   to the saved ar.bspstore. Thus: we save ar.rnat in setjmp()
   and simply restore ar.bspstore and ar.rnat in longjmp().

This code needs a cleanup.