Re: C23 support in Autoconf

[Antonin Décimo]

I wasn't there when the magic was written, but I would have expected
AC_PROG_CC_C89, AC_PROG_CC_C99 and possibly new AC_PROG_CC_Cx macros
to select a version of the C standard. Apparently that wasn't their
job and now they've been deprecated in 2.70.