PATCH: new "void" memory region attribute

[Greg McGary]

Michael Snyder <msnyder@redhat.com> writes:

> Greg McGary wrote:
> > 
> > Add "void" attribute, which disallows both read & write access.  This
> > useful for guarding holes in a target's address space that cause the
> > system to hang when read/written.
> > 
> > OK to commit?
> 
> I like it.  Would you consider adding a test to the testsuite?

Surely.  Thanks for the invite.  Having never hacked the gdb testsuite
before, I look forward to sleuthing it out.  8^)

I'll post diffs for the test case, then commit the whole wad when
that's approved.

Greg