Fix the string representation of functions exported from asm.js modules
in the presence of imported functions.

R=jkummerow@chromium.org

Bug: chromium:1045767, chromium:667678
Change-Id: I55714252036511598eeec7fe7b81985213f7e4f2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2022142Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65993}