According to ES#sec-built-in-function-objects all built-in functions
must be strict.

This is a preliminary CL before changing the way we define built-in
functions in native JS files.

Bug: v8:6459
Change-Id: I8e60b342f04ea1b0843fe1990334cbb9b26ebac4
Reviewed-on: https://chromium-review.googlesource.com/546215Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46237}