Utility function to map error codes to a string

Many projects are rolling their own and most of them end up with missing error codes over time. Should we provide an official solution?

An example of the many such discussions I've been pointed to: https://stackoverflow.com/questions/24326432/convenient-way-to-show-opencl-error-codes#comment39780932_24336429

No source files, tests, or entry points are named in the issue. Start by reviewing the linked Stack Overflow discussion and clarifying the scope of an official error-code mapping API; done should include an agreed design and complete error-code coverage.

Written by the indexing model from the issue text.