In the build for apache2filter, there is some AIX-specific
logic to set EXTRA_LDFLAGS:

APXS_SBINDIR=`$APXS -q SBINDIR`
EXTRA_LDFLAGS="$EXTRA_LDFLAGS \ -Wl,-bI:$APXS_SBINDIR/httpd.exp"

Problem:

1) With Apache 2.0, httpd.exp is in the libexec dir, not 
   the sbin dir, so the link step fails.

2) Once the path for httpd.exp is tweaked, the DSO is built
   but run-time linking is not enabled so PHP segfaults
   the first time it tries to call an APR function
   (httpd.exp doesn't have apr_ stuff in it; run-time
   linking is used to resolve APR references)

   The fix for that is to add -Wl,-brtl to the link step.

For my own gcc build I had to include -L/path/to/libgcc.a -lgcc in EXTRA_LDFLAGS to resolve references to some arithmetic operations, but I doubt that is something for PHP to worry about.

So here is a patch to sapi/apache2filter/config.m4
(tested with 4.3.0, but CVS HEAD looks like patch should apply fine there too).

See http://www.apache.org/~trawick/php.patch1

A funny thing about existing code in the area of the patch
is the use of $(INSTALL_ROOT) in front of directories printed by "apxs -q"...  I don't see how that makes any
sense, but for my builds INSTALL_ROOT was unset so it
worked.

Here is a line from config.m4 that has an example of
this use of $(INSTALL_ROOT):

APXS_LIBEXECDIR='$(INSTALL_ROOT)'`$APXS -q LIBEXECDIR`

My patch depends on the setting of APXS_LIBEXECDIR.