With HP-UX (Rel. 11.0, s700, PA1.1) exim's (v3.03) build process doesn't
work as straight as it used to do in earlier versions.
After adding "CC=cc" and changing "CFLAGS=-O" to "CFLAGS=-O -Ae -DHPUX" in
OS/Makefile-HP-UX and rebuilding the Makefiles all ran fine.
I don't really think that there are many souls out there using gcc on a
HP-UX machine, but if you want to make the scripts decide then simply let
it check for /opt/ansic (or /opt/ansic/bin/cc).