sim: use AC_REQUIRE with AC_PROG_CC

sim: use AC_REQUIRE with AC_PROG_CC

The autoconf guys point out that our usage of AC_PROG_CC in the
SIM_AC_COMMON does not jive with their intended use.
	http://www.gnu.org/software/autoconf/manual/autoconf.html#Expanded-Before-Required

So utilize AC_REQUIRE to make the warnings go away and generate
the correct code with different autoconf versions.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>