Hello Vincent,

Did you do any additional steps other than configure and make?
I mean, at least, I was able to compile ruby 1.8.6p111 on AIX 5.3
using gcc 4.2.3.

I just issue these commands after extracting the tar ball.
% ./configure --with-openssl-dir=/opt/freeware
--with-zlib-dir=/opt/freeware --with-readline-dir=/opt/freeware
--prefix=$HOME/r186p111 --disable-ipv6

% make

% make install

% ruby -v
ruby 1.8.6 (2007-09-24 patchlevel 111) [powerpc-aix5.3.0.0]

% gcc -v
Using built-in specs.
Target: powerpc-ibm-aix5.3.0.0
Configured with: ../gcc-4.2.3/configure --prefix=/home/kanemoto/gcc423
--enable-shared --enable-threads=aix --enable-languages=c,c++
Thread model: aix
gcc version 4.2.3

% oslevel -s
5300-06-03-0732

Best regards,
-- 
Yutaka KANEMOTO
http://d.hatena.ne.jp/kinpoco/