The mksnapshot-specific runtime flag --target-arch, together with
--target-os, specifies the target platform for the generated embedded.S
file.

Bug: v8:9103
Change-Id: Icb03a381101e7ab0db4a5fbbf3be8e23ed0b1a1c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1624165
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61739}