RFC: Changing AC_PROG_CC to AC_PROG_CC_C99 in top level configure

[Mike Frysinger]

On 26 Apr 2021 19:32, Joseph Myers wrote:
> On Mon, 26 Apr 2021, Nick Clifton via Gcc-patches wrote:
> >   Given that gcc, gdb and now binutils are all now requiring C99 as a
> >   minimum version of C, are there any objections to updating
> >   configure.ac to reflect this ?
> 
> This isn't an objection, since upgrading auto* for the toolchain can be 
> complicated, but note that AC_PROG_CC_C99 is obsolete in Autoconf 2.70 and 
> instead AC_PROG_CC enables C11 mode if supported.  (So moving to the 
> latest Autoconf and Automake releases would supersede this change.)

considering how long it took before we adopted 2.69, seems unlikely we can
upgrade to 2.70.  plus, i think there was a flurry of regression fixes for
2.70, and ideally we'd get a 2.71 ?

as long as we have 2.69, we should move to AC_PROG_CC_C99 in all projects.
-mike