The native (bundled) compiler for HPUX currently will not work,
because it is not a full ANSI C compiler. The optional ANSI C
compiler should work as long as you give it the
./configure CC='cc -Ae'). This is equivalent to
./configure CC='c89 -D_HPUX_SOURCE', which was the previous
recommendation. This has only been tested recently for HPUX 10.20.