[DynInst_API:] Pruning former platform support

[Josh Stone <jistone@xxxxxxxxxx>]

As I look for minor tasks that I can help with, one possibility is to
clean up platforms that used to be supported, but are no longer.

First looking at arch_* macros, arch_alpha and arch_mips have just one
tiny occurrence each, and seem like obvious things to prune.

There are more os_* macros.  I think os_freebsd, os_linux, os_windows,
and all the os_bg* platforms are the only ones with active support.
That leaves os_aix, os_irix, os_osf, os_solaris, and os_vxworks which
seem to not be supported anymore.

So, would patches be acceptable to remove code for these platforms?  As
a first pass, I just intend to look around those mentioned macros, and
any source files that were completely specific to those platforms.
Later we might approach it a little more deeply, for example by removing
unneeded abstractions.


Josh