[RFC] HP-UX native support

[Michael Chastain]

Some scraps of thought:

In general, I'm okay with dropping support for follow-fork and
other hpux-only features.

Most of the PR's for hp-ux are about build problems, rather than
advanced features.  So if building gdb gets better or stays the
same, that's okay.

hpux 10.20 is obsolete and HP no longer supports it.
However, many people still use it.

gdb has to work on hpux 11.00 and hpux 11.11 as well.
I can take care of testing those.

Michael