Assumes that (is_clang = false && is_win) => Windows native (MSVC).

Cross-compile builds will use clang and not the native tools and thus
not fall into this category.

This CL adds x86 and x64 MASM trampolines that can be used with the
native Windows toolchain (ml.exe, ml64.exe), when using is_clang =
false.

This reverts commit 8e4a5e97.

Bug: chromium:1056170
Change-Id: I7204f15898ec5eddcc5892d4d08266a69d84ab85
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2139211
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67036}