Previously only AssemblerOptions created by AssemblerOptions::Default()
could have inline_offheap_trampolines set to true.

This fixes OutOfLineTruncateDoubleToI from generating calls via the
DoubleToI trampoline.

Bug: v8:9338
Change-Id: Ia4638cd185e9041c7c69996783d0ce5600e9723a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1662288Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62213}