Actually a fix as much as a bug.  I compiled apache 2.0.36 and php 4.2.1 with no difficulties.  Yet when I migrated from 2.0.36 to 2.0.39 it php no longer compiled cleanly.  It failed on the following file:

php4.2.1/sapi/apache2filter/php_functions.c

I had to comment out the following block:

#if !MODULE_MAGIC_AT_LEAST(20020506,0)
                ADD_STRING(boundary);
#endif

After this block was commented out it compiled as normal.  Please indicate what does this block do?

I compiled php with the following options:

./configure --with-apxs2=/usr/local/apache/bin/apxs \
        --with-config-file-path=/usr/local/apache/conf \
        --enable-debug=no \
        --enable-yp \
        --with-java=/usr/local/java \
        --with-mcrypt=/usr/local/bin \
        --enable-track-vars

and apache with the following options:

./configure --prefix=/usr/local/apache --enable-shared=max --enable-access --enable-auth --disable-auth-anon --enable-include --enable-mime-magic --enable-cern-meta --enable-expires --enable-headers --enable-usertrack --enable-unique-id   --enable-ssl  --enable-info  --with-ssl=/usr/local/ssl 
--enable-modules="rewrite speling ssl" 
--enable-module=most