STR:
1. Open the project
2. Observe "Test.cs" contents
3. Observe the "Unreachable code" displayed as both error and a warning

Expected: "Unreachable code" warning is thrown into console window

Actual: "Unreachable code" appears as both warning and error, thus doesn't allow building/entering play scene.

Note: Declaring a variable "int a;" in Start() method causes warning "The variable `a' is declared but never used" to be displayed as both error and warning too.

Reproduced on: 5.2.5f1, 5.3.6p8, 5.4.2f2