Give a better error for PCH with exec-shield-randomize

[Geoff Keating]

> From: Ian Lance Taylor <ian@wasabisystems.com>
> Date: 04 Mar 2004 20:55:20 -0500

> host-darwin.c goes ahead and
> calls munmap on space which it doesn't need, but it only does that in
> the special case of actually reading a PCH file, not in the normal
> case of no PCH file.

That's not correct; it always calls munmap (or equivalent).  If no PCH
file is used, then as soon as that is certain the address space is
released.  As documented for HOST_HOOKS_GT_PCH_USE_ADDRESS:

> If no PCH will be loaded, this hook may be called with @var{size}
> zero, in which case all reserved address space should be freed.

-- 
- Geoffrey Keating <geoffk@geoffk.org>