configure error ... not set in the previous run

[John Calcote]

I've got a friend at work that's experiencing this problem while 
building an apache distribution:

...
utilities/agctl/Makefile.am:16: compiling `agctl.c' with per-target 
flags requires `AM_PROG_CC_C_O' in `configure.in'
Makefile.am: installing `./INSTALL'
Running autoconf ...
Running ./configure --config-cache --enable-maintainer-mode 
--enable-compile-warnings --with-apache=/opt/novell/apache2 
--prefix=/opt/novell/access-manager 
--sysconfdir=/etc/opt/novell/access-manager --libdir=/opt/novell/lib ...
configure: WARNING: unrecognized options: --enable-compile-warnings
configure: loading cache config.cache
configure: error: `CFLAGS' was not set in the previous run
configure: error: in `/usr/src/packages/BUILD/novell-apache-gateway-1.0.0':
configure: error: changes in the environment can compromise the build
configure: error: run `make distclean' and/or `rm config.cache' and 
start over
error: Bad exit status from /var/tmp/rpm-tmp.91236 (%build)

He's wondering (and so am I) what the error, "configure: error: `XYZ' 
was not set in the previous run" means.

Thanks,
John