Since HPUX now exists for Itanium, we should decouple the assumption

that OS=hpux is the same as CPU=hppa.  First steps at doing this.
With these patches, we still work on hppa with either gcc or HP's cc.
We might work on hpux/itanium with gcc, but I can't test it.  Definitely
will not work on hpux/itanium with non-gcc compiler, for lack of spinlock
code.