How to prevent -O2 in CFLAGS?

[Grégoire Sutre <gregoire.sutre%gmail.com@localhost>]

Hi,

I'm trying to update a pkgsrc-wip package, but the new source fails to
build within pkgsrc (direct ./configure && gmake works fine).  It turns
out that this is due to CFLAGS containing `-O2' when the package is
configured via pkgsrc:

/usr/bin/env [...] CC=gcc 'CFLAGS=-O2 -pipe -I/usr/pkg/include [...]' 
/bin/sh './configure' [...]

Hopefully this problem will be solved upstream.  But, still, I'd like
to know how to prevent CFLAGS from containing `-O2', and, in general,
how to control the setting of CFLAGS.

Thanks for the help,

Grégoire