The web appears to depend on being able to redeclare functions-in-blocks
in sloppy mode (examples seen so far tend to redeclare identical functions,
most likely accidentally).

This patch opens a minimal hole: two same-named function declarations
in the same scope are allowed, only in sloppy mode.

BUG=v8:4693, chromium:579395
LOG=y

Review URL: https://codereview.chromium.org/1622723003

Cr-Commit-Position: refs/heads/master@{#33478}