autoupdate replacing AC_PROG_CC_C99 should not use AC_REQUIRE

[email protected]

Synopsis: autoupdate causes botched 'configure' result from
'AC_PROG_CC_C99' in configure.in

User workaround: After running autoupdate I found it necessary to remove
the "AC_REQUIRE()" that you have wrapping the AC_PROG_CC
Otherwise the buildconf produces a configure that has problems

*Summary:* > When running autoupdate on an older configure.ac, the tool
correctly identifies AC_PROG_CC_C99 as obsolete but incorrectly replaces it
with a block containing AC_REQUIRE([AC_PROG_CC]) at the top-level of the
script. This causes a fatal M4 expansion error because AC_REQUIRE cannot be
used outside of an AC_DEFUN block.

*Steps to Reproduce:*

   1.

   Start with a configure.ac containing a top-level AC_PROG_CC_C99.
   2.

   Run autoupdate.
   3.

   Attempt to run autoreconf or ./buildconf.sh.

*Actual Results:* autoupdate produces:
Code snippet

m4_warn([obsolete], [AC_PROG_CC_C99 is obsolete; use AC_PROG_CC])dnl
AC_REQUIRE([AC_PROG_CC])

Resulting in error: error: AC_REQUIRE(AC_PROG_CC): cannot be used outside
of an AC_DEFUN'd macro.

*Expected Results:* It should simply replace the obsolete macro with
AC_PROG_CC when detected at the top-level.

*Environment:* Ubuntu 24.04 LTS, Autoconf version 2.71