When building v8 using MSVC (as for Node.js), clang-cl is not available
to act as an assembler. This change allows mksnapshot to accomodate this
fact by emitting assembly in the MSVC ARM assembler's format.

Incidentally, the MSVC ARM asm format is just the ARM, Holdings assembler's
asm format with a small handful of unimplemented features.

https://docs.microsoft.com/en-us/cpp/assembler/arm/arm-assembler-reference

Bug: chromium:893460,v8:8645
Change-Id: I1a6b765b0f9b4d117d7a6f100015a4f124442865
Reviewed-on: https://chromium-review.googlesource.com/c/1394758
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58842}