After support for ARCH_PPC was dropped, it became a subset of
ARCH_PPC64. If you compile for ppc64, then you set the ARCH_PPC64
define which also sets the ARCH_PPC define.
To be able to again support ppc (32 bit) those defines should be
split up again.

This commit only splits up the defines but does not introduce a
working ARCH_PPC variant.

Bug: v8:10102
Change-Id: I64e0749f8e5a7dc078ee7890d92e57b82706a849
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1989826
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Milad Farazmand <miladfar@ca.ibm.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66390}