Hi, I got this symptom by compiling PHP:
/usr/bin/sh ../libtool --mode=compile xlc -DHAVE_CONFIG_H \
-I. -I. -I../main   -DXML_BYTE_ORDER=21  -qsource \
-qshowinc -c zend_extensions.c
xlc -DHAVE_CONFIG_H -I. -I. -I../main -DXML_BYTE_ORDER=21 \
-qsource -qshowinc -c zend_extensions.c
"zend_extensions.c", line 33.16: 1506-068 (S) Operation between types "void*" and "int" is not allowed.

 I use the xlc-version of the C Set ++ for AIX compiler, as it is more ANSI-C than the cc-version. It also shows more errors.
 My configuration of PHP (as a CGI-program to be used by Lynx):
CC=xlc ./configure --prefix=/home/pistoor/php \
  --with-config-file-path=/home/pistoor/php --enable-debug \
  --enable-sigchild --enable-calendar --enable-ftp \
  --enable-trans-sid --enable-shmop --with-regex=php \
  --enable-sysvsem --enable-sysvshm --enable-wddx \
  --enable-yp
 I found, that the prototype of dlopen was missing. It is standing in /usr/include/dlfcn.h.
 In config.log, I found these lines:
configure:44766: checking for dlfcn.h
configure:44776: xlc -E  -DXML_BYTE_ORDER=21 conftest.c >/dev/null 2>conftest.out
"conftest.c", line 1.7: 1506-219 (W) #line value 44771 too large.
configure: failed program was:
#line 44771 "configure"
#include "confdefs.h"
#include <dlfcn.h>
 So configure guessed wrongly, dlfcn.h would be missing.

 I edited config.cache and rerun configure.
 Now I got another compile failure later. :-)

 Regard
 Andreas Pistoor