Off-heap trampolines (short trampolines that jump to .text-embedded
builtin instruction streams) should contain exactly one OFF_HEAP_TARGET
reloc entry.

When AddAnonymousCode is called on such a trampoline, it copies the
(off-heap) *instruction stream* and thus should never perform any
relocations using the *trampoline's* RelocInfo.

Bug: v8:6666
Change-Id: I09a11344fb7e62d759c4c943712e7d4e91199130
Reviewed-on: https://chromium-review.googlesource.com/1179671Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55214}