Split out embedded file writers for AIX, Windows, and macOS. These are
no longer selected by compile-time defines (e.g. V8_OS_WIN,
V8_TARGET_ARCH_X64) but by --target-os and --target-arch runtime
flags.

Bug: v8:9103
Change-Id: I5d5cac15e48b5c743d74f8a382606a6194ba7865
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1624216
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61785}