Undetected unreachable code

These are obvious mistakes. <!-- Please try to reproduce the issue with the latest published version. It may have already been fixed. For npm: `typescript@next` This is also the 'Nightly' version in the playground: http://www.typescriptlang.org/play/?ts=Nightly --> **TypeScript Version:** 3.7.x-dev.20191221 <!-- Search terms you tried before logging this (so others can find this issue more easily) --> **Search Terms:** **Code** ```ts declare const a: boolean; (() => { if (a) return; if (a) { return; // Unreachable } }); while (1) { if (a) break; if (a) { break; // Unreachable } } ``` **Expected behavior:** Detect unreachable code. **Actual behavior:** not detected. **Playground Link:** http://www.typescriptlang.org/play/index.html?ts=3.8.0-dev.20191221#code/CYUwxgNghgTiAEYD2A7AzgF3lAXPARkkhCFCgNwCwAUABS0CU8AvAHzwDeN8P8AlgDN4tKEzgYArjArdeg4aM6zevcVIrwA9JvgBVFHChgAFlHwll8AL40rDKtQDuxviWEBGJl2or5IpviGANYOvkL+Sj4qvIGkIVo6+oYmZhZRPDbUVkA **Related Issues:** <!-- Did you find other bugs that looked similar? -->