Honor --harmony-regexp-property flag.

R=hablich@chromium.org
BUG=v8:4926
LOG=Y

Review URL: https://codereview.chromium.org/1899153002 .

Cr-Commit-Position: refs/branch-heads/5.0@{#40}
Cr-Branched-From: ad16e6c2cbd2c6b0f2e8ff944ac245561c682ac2-refs/heads/5.0.71@{#1}
Cr-Branched-From: bd9df50d75125ee2ad37b3d92c8f50f0a8b5f030-refs/heads/master@{#34215}