Reland "move conditions for JIT into SkVM.h"

This is a reland of 166cd52cee64fb59a1c8daad379feca2e18d723a
with iOS simulator builds disabled.

Original change's description:
> move conditions for JIT into SkVM.h
>
> This makes it easier to keep in sync with the implementation in
> SkVM.cpp, and it's easier to handle here once than in each build system.
>
> Change-Id: I429f90cfc16f35a0d7e0b0fde176bc013aa7db18
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310263
> Commit-Queue: Mike Klein <mtklein@google.com>
> Commit-Queue: Herb Derby <herb@google.com>
> Auto-Submit: Mike Klein <mtklein@google.com>
> Reviewed-by: Herb Derby <herb@google.com>

Change-Id: I82837c3d959769f26197f2402d3b911e71a35675
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/310465
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed