Add automated testing: Negative compiler tests

[cpurdy]

Is your infrastructure request related to a problem? Please describe. (Include any links to
other related issues.)
We need a suite of tests for things that the compiler is supposed to reject. This is important because breaking changes go unnoticed, because we're not verifying that the compiler correctly reports errors. (We're generally only testing the positive cases, not the negative cases.)

Describe the solution you'd like
Requirements: (i) Automated. (ii) Easy to add tests. (iii) Obvious reporting.

Describe alternatives you've considered
We have considered: Each test consisting of a source file (or source directory) and a separate file indicating the expected compiler error.

Additional context
Gene has a small collection of negative tests that he periodically verifies by hand.