This test started failing on arm64-debug-nosnap builds since we'd have
leftover NEVER_EVACUATE code-space pages from Isolate initialization.

Ensure that we exhaust all such pages and overflow into LO_SPACE before
continuing into the real test, and simply generate dummy code instead of
copying a fake CEntryStub.

Bug: v8:6690
Change-Id: I3889b5818e2467dcdce3485f1372f3b7383478f4
Reviewed-on: https://chromium-review.googlesource.com/608139Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47273}