Disabling optimization

[Jonathan]

My autoconf/automake project is optimizing by default with "-g -O2". 
Unfortunately, we have verified that this is causing a run-time error
by overriding CXXFLAGS in Makefile.am with just "-g".  With the "-O2"
flag removed, everything works great.

I have been trying to find out where this "-O2" is coming from so I
can disable it at the configure.ac level, but my attempts have been
fruitless.

How do I disable the "-O2" flag in the most portable way possible?  

I'm developing on Linux with autoconf 2.59, automake 1.6.3, libtool
1.5.2, gcc 3.3.4.

-- 
-Jonathan