Get a working ast-ksh build for SunOS using c99 and defining _XPG6
(and __EXTENSIONS__ for strict STDC).  Also needs -lm.
Fix testing to work prior to [stage-]install. No revbump needed.
okay'd by jperkin@
NB there are still some corner cases not working on some SunOS, but
on illumos SunOS 5.11 this actually goes a real long way over stock sh/ksh!

(richard)