Add a Lint hadrian rule and an .hlint.yaml file in base

Background: #18424

It implements:

• A Hadrian rule to run a premade hlint command line over the base/ directory, with proper include paths;
• Utilities to signal a failure in a Hadrian rule. It is based on the same model as putSuccess;
• A light syntactic fix to Unsafe.Coerce to allow for proper parsing by hlint, disambiguating from a CPP instruction.