This reverts commit 3d023952.

Reason for revert: breaks gcc build

Original change's description:
> [runtime] Make JSFunction::prototype_or_initial_map field optional.
> 
> Functions that don't have prototype need to store neither prototype nor
> initial map, so the |prototype_or_initial_map| field is not required for
> such maps.
> 
> Bug: v8:6459
> Change-Id: I4b3066bd6a4fed42c19f217bae82a8bce552bdca
> Reviewed-on: https://chromium-review.googlesource.com/570250
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46840}

TBR=jkummerow@chromium.org,jarin@chromium.org,ishell@chromium.org

Change-Id: Ie9951c87b15c8bd365ed187d7f719b8f08dd0bb5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6459
Reviewed-on: https://chromium-review.googlesource.com/583088Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46841}