When compiling open source on HPUX, try these steps:

1.) Make sure you have the linker patch (PHSS_26559 or later) installed
on the OS.

2.) Use GNU C compiler, not HP ANSI C.

3.) Use GNU build tools (and versions) m4 1.4, automake 1.5, autoconf
2.52, libtool 1.4

4.) Before compiling PHP, hack the apxs script to change the DSO
extension. This must be done in 2 places:
change the line: my $dso_ext = "so";
to: my $dso_ext = "sl";
and
change the line: $d =~ s|\.so$||;
to: $d =~ s|\.sl$||;

5.) Add thread local storage support with the following lines in
apachectl:

#ADD THREAD LOCAL STORAGE SUPPORT TO HPUX IN APACHECTL SCRIPT:
export SHLIB_PATH=$ORACLE_HOME/lib:/opt/apache/lib:$SHLIB_PATH
export LD_PRELOAD=/usr/lib/libpthread.sl:/usr/lib/libcl.sl

One final note, on HPUX you are better off using HP's Apache
distribution, which is available for free off their site at:
http://www.hp.com/products1/unix/webservers/apache/downloads/index.html

It has been optimized for the HPUX platform and is quite easy to set
up.

Good luck,