Update autoconf for gas

[DJ Delorie]

Looks OK to me.  Tested?

> Is this OK?
> 
> -- 
> Daniel Jacobowitz
> MontaVista Software                         Debian GNU/Linux Developer
> 
> 2003-08-28  Daniel Jacobowitz  <drow@mvista.com>
> 
> 	* configure.in: Update AC_PREREQ to 2.57.  Use AC_CONFIG_FILES
> 	and AC_CONFIG_COMMANDS instead of the three-argument AC_OUTPUT.
> 	* configure: Regenerated with autoconf 2.57.
> 	* aclocal.m4: Regenerated with aclocal-1.7.
> 	* Makefile.in, doc/Makefile.in: Regenerated with automake-1.7.