As Dan writes, I too survive work by using [Gentoo Prefix][2].

%% uname -a
HP-UX localhost B.11.31 U 9000/800 HP-UX
%% gcc --version
gcc (GCC) 4.2.4 (Gentoo 4.2.4-r01.2 p1.1)
%% bash --version
GNU bash, version 4.0.35(1)-release (hppa2.0n-hp-hpux11.31)
%% ls --version                                          
ls (GNU coreutils) 8.1
Packaged by Gentoo (8.1 (p1))

Thanks to haubi for putting effort into the necessary upstream changes/patches for hppa-hpux support!

[2]: http://www.gentoo.org/proj/en/gentoo-alt/prefix/