[RFC] Rework mem_barrier() definitions in compiler.h

[Alan Coopersmith]

Mark Kettenis wrote:
>> Date: Tue, 4 Aug 2009 02:14:55 -0400
>> From: Matt Turner <mattst88 at gmail.com>
>>
>> As noted by the numerous XXX markers, there are quite a few issues,
>> outlined here.
>>
>> o what the heck is the stuff wrapped in 'defined(__powerpc__) &&
>> !defined(__OpenBSD__)'?
> 
> No idea; Alan Coopersmith added that check fairly recently, but I fail
> to see why.

Having them there and _X_EXPORT'ed on other platforms was causing build
failures because they were being added to the symbol list by pcpa's
symbol visibility changes, which at least on Solaris caused linker failures
with references to non-existent symbols.

I made them #if defined(__powerpc__) && !defined(__OpenBSD__) because that
was the test for exporting those symbols previously in
hw/xfree86/loader/xorgsym.c before pcpa's change in commit
b1dac41fb3853ca8182048ea57b88b6e84ecceb3.

-- 
	-Alan Coopersmith-           alan.coopersmith at sun.com
	 Sun Microsystems, Inc. - X Window System Engineering