tce-load -i compiletc

cd ilmbase-2.3.0

CC="gcc -flto -fuse-linker-plugin -march=i486 -mtune=i686 -Os -pipe" CXX="g++ -flto -fuse-linker-plugin -march=i486 -mtune=i686 -Os -pipe" ./configure --prefix=/usr/local --disable-static --localstatedir=/var

[-fno-exceptions fails]

find . -name Makefile -type f -exec sed -i 's/-g -O2//g' {} \;

make
sudo make install

Summary for IlmBase features:
enable large stack optimizations             yes
ISO C++ Standard                             14

internal library namespaces                  Imath_2_3
                                             Iex_2_3
                                             IlmThread_2_3

public namespaces                            Imath Iex IlmThread