Is there any way to disable compiler optimization and enable debug?

HI,
I would like to debug PG because I have a problem when I run initdb, and
I have question about the configure file.

when I used the command below to config PG, it was only built with
debugging symbols (-g) and O2 compiler optimization which would lead to
execute order not match the source code order.
./configure --enable-debug --enable-depend --enable-cassert
--prefix=/home/pgsql/pgsql

then I export CFLAGS=O0, but it still couldn't work.
I read a little about confiqure file and find out that CFLAGS is unset in
confiqure.
and CFLAGS is also control by global variable: ac_env_CFLAGS_set and
ac_env_CFLAGS_value.

but i do not know how i could pass ac_env_CFLAGS_set and
ac_env_CFLAGS_value to the configure file.

by now, I replace all the O2 flag to O0 in configure file to resolve the
debug source code order problem temporary.

Is there any other way to disable compiler optimization and enable debug?

Thank you for help.