Pipeline::GenerateCodeForWasmNativeStub() currently does not pass
an Isolate to the PipelineData it creates, to ensure that compiled
code does not accidentally depend on a given Isolate. However, this
prevents the assembler from converting ExternalReference accesses to
RootArray offsets. This patch sets the corresponding AssemblerOption.

Bug: v8:3770
Change-Id: Ia4d5269e2e884a0af8abc6d122734f47db045ac0
Reviewed-on: https://chromium-review.googlesource.com/c/1404447Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58700}