Add feature for treating compiler errors as warnings

[dcecile]

I'm getting the "is a compiler macro and no longer needs to be imported" warning in my code and want an automated way to make sure we don't introduce more instances.

Other compilers support features like -Werror where compiler warnings are treated as errors. Could the Vue SFC compiler get the same feature?

Writing every compiler warning as an ESLint rule could work but seems a bit backward.