configure.ac: Update AC_PROG_CC and AC_PROG_LEX for autoconf 2.70

With autoconf 2.70 we must use AC_PROG_CC (which will check for c11
and c99), for earlier versions we'll use AC_PROG_CC_C99. Also use
AC_PROG_LEX([noyywrap]), the extra argument is ignored with earlier
versions, but required for 2.70.

Signed-off-by: Mark Wielaard <mark@klomp.org>
2 files changed