This patch turns on ES2015-style function hoisting semantics in
staging. --harmony_sloppy_function was previously staged, leading
to a number of bugs being filed and the staging being reversed;
important bugs have been fixed, so it is time to try again.

R=adamk
LOG=Y
BUG=v8:4285

Review URL: https://codereview.chromium.org/1393423002

Cr-Commit-Position: refs/heads/master@{#31190}