Debug builds add -std=c99 (or -xc99 for suncc) to CFLAGS
(AX_CFLAGS_WARN_ALL_ANSI configure macro).

Non-debug builds do not invoke AX_CFLAGS_WARN_ALL_ANSI checks and
therefore won't have C99 support enabled, which breaks the build of
mod_http_cache due to "for (int i... )"-style C99 loops.

NOTE: AC_PROG_CC_C99 would make a lot of sense here and MSVC (2005)
accepts "for (int ...)" constructs too.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>