Enforcing strict c99 compliance

[Adam Mercer]

Hi

In a project I am involved with we are in the process of moving from
ANSI C89 to C99, the first step in this transition was to use
AC_PROG_CC_STDC to detect the compiler instead of AC_PROG_CC (we can't
use AC_PROG_CC_C99 as there are legacy systems running autoconf-2.59
that we need to support). On more modern system this causes the
-std=gnu99 flag to be automatically added, but not on the older
systems which AFAICT support C99 (at least the parts of the C99 spec
we are interested in utilising).

Checking through config.log it seems that no C99 checks are being
performed, how can I find out why these tests are not being performed?

Is there a macro that I can use to enforce strict c99, i.e. pass
-std=c99 (instead of -std=gnu99) or do I need to do this manually?

Cheers

Adam