Conflicting function return types checked for single bindings, but not overloads.

<!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨 Half of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Even if you think you've found a *bug*, please read the FAQ first, especially the Common "Bugs" That Aren't Bugs section! Please help us by doing the following steps before logging an issue: * Search: https://github.com/Microsoft/TypeScript/search?type=Issues * Read the FAQ: https://github.com/Microsoft/TypeScript/wiki/FAQ Please fill in the *entire* template below. --> <!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --> **TypeScript Version:** 3.1.1-insiders.20180926 (what's running in the playground) <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** conflicting function return **Code** ```ts declare var foo: () => number declare var foo: () => string declare function bar(): number declare function bar(): string ``` **Expected behavior:** `foo` and `bar` to both fail **Actual behavior:** `bar` seems to still type-check, inconsistently with `foo` **Playground Link:** https://www.typescriptlang.org/play/index.html#src=declare%20var%20foo%3A%20()%20%3D%3E%20number%0D%0Adeclare%20var%20foo%3A%20()%20%3D%3E%20string%0D%0A%0D%0Adeclare%20function%20bar()%3A%20number%0D%0Adeclare%20function%20bar()%3A%20string **Related Issues:** N/A