The motivation behind this is that MSVC doesn't support inline assembly
on x64. Emitting the embedded blob as a plain assembly file will give us
MSVC support (and possibly faster compilation times as a side-effect).

Bug: v8:6666,v8:8349
Change-Id: I2e6cf072faa9ef406fe721a05b63912c655546c2
Reviewed-on: https://chromium-review.googlesource.com/c/1329205
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57524}