I'm compiling PHP 4.2.1 with:

./configure --with-config-file-path=/usr/local/etc \
--with-layout=GNU \
--with-apxs=/usr/local/sbin/apxs \
--enable-dependency-tracking \
--with-openssl=shared \
--enable-libgcc=shared \
--with-zlib-dir=/usr \
--with-zlib=shared \
--with-aspell=/usr \
--enable-bcmath=shared \
--with-bz2=shared \
--enable-calendar=shared \
--with-crack=shared \
--with-curl=shared \
--enable-dba=shared \
--with-gdbm=shared \
--with-ndbm=shared \
--with-db2=shared \
--with-db3=shared \
--enable-dbase=shared \
--enable-dbx=shared \
--enable-dio=shared \
--with-dom=shared \
--with-dom-xslt=shared \
--with-dom-exslt=shared \
--enable-exif=shared \
--enable-filepro=shared \
--enable-ftp=shared \
--with-tiff-dir=/usr \
--with-jpeg-dir=/usr \
--with-png-dir=/usr \
--with-xpm-dir=/usr/X11R6 \
--with-freetype-dir=/usr \
--with-gd=shared,/usr/gd-with_gif/ \
--enable-gd-native-ttf=shared \
--with-gettext=shared \
--with-gmp=shared \
--with-icap=shared \
--with-iconv=shared \
--with-imap=shared \
--with-kerberos \
--with-imap-ssl \
--with-java=/usr/java/j2sdk1.4.0 \
--with-ldap=shared \
--enable-mbstring=shared \
--enable-mbstr-enc-trans \
--enable-mbregex \
--with-mcal=shared \
--with-mcrypt=shared \
--with-mhash=shared \
--with-pdflib=shared \
--with-pgsql=shared \
--with-pspell=shared \
--with-recode=shared \
--with-mm=shared \
--enable-shmop=shared \
--enable-sockets=shared \
--with-regex=php \
--enable-sysvsem=shared \
--enable-sysvshm=shared \
--enable-tokenizer=shared \
--enable-wddx=shared \
--with-xmlrpc=shared \
--enable-xslt=shared \
--with-xslt-sablot=shared,/usr \
--with-expat-dir=/usr \
--with-sablot-js=shared,/usr \
--enable-yp=shared \
--with-zip=shared \
--enable-versioning=shared \
--enable-shared=shared \
--enable-inline-optimization=shared \
--enable-memory-limit=shared

I added '=shared' to so many of the options because the compile documentation sucks my left testicle, and it was faster to add '=shared' to a bunch of the options than read through the 'configure' script for hours to determine which options are actually affected by '=shared'.

Anyways, the 'configure' script completed successfully, and I went ahead with 'make'.  After a few minutes, I got this error:

internal_functions.c:53: `phpext_ps_mm_ptr' undeclared here (not in a function)
internal_functions.c:53: initializer element is not constant
internal_functions.c:53: (near initialization for `php_builtin_extensions[9]')

I examined 'main/internal_functions.c' and found this:

zend_module_entry *php_builtin_extensions[] = {
	phpext_xmlrpc_ptr,
	phpext_xml_ptr,
	phpext_standard_ptr,
	phpext_posix_ptr,
	phpext_pcre_ptr,
	phpext_openssl_ptr,
	phpext_mysql_ptr,
	phpext_ctype_ptr,
	phpext_aspell_ptr,
 phpext_ps_mm_ptr,
};

First, just to try, I cleaned up the code, removing that trailing comma after 'phpext_ps_mm_ptr'.  But, as I suspected, that did nothing.

Then I noticed all the #INCLUDEs just above the declaration for 'php_builtin_extensions[]', noticing that they tended to correspond with the elements of 'php_builtin_extensions[]'.  So I determined to find in which header file 'phpext_ps_mm_ptr' was being defined with 'grep -r phpext_ps_mm_ptr *'.

I found it being defined in 'ext/session/mod_mm.h'; which, for some reason or another, wasn't be #INCLUDEd in 'main/internal_functions.c'.  So I added the following line:

#include "ext/session/mod_mm.h"

Running 'make' again, 'main/internal_functions.c' compiled just fine.  Except now 'main/internal_functions_cli.c' failed compilation with the same error--and, consequently, the same fix.

Anyways, that's it.