Automatically test equivalence of optimized IR with unoptimized IR

The current equivalent test requires the user to create an entry function. This has a few downsides:

- requires more work from the user
- requires the user to understand how to create such an entry function

cdleary@ and I propose instead that:

By default, all functions in a module are tested (this is to encourage testing). Build options are added so that:

- the user can turn off equivalence testing for all functions in the module
- the user can supply a list of functions that are not tested (and the rest are). Useful in the case where most functions are tested fast enough but a few take forever to test.
- the user can supply a list of functions that are tested (and the rest are not). Useful in the other case where most functions are tested slowly but a few are tested quickly (or *must* be tested).

These 3 options are mutually exclusive.