Restore the ability to build run-pass/run-fail/bench tests without running them

[brson]

Some of our tests have a default mode for running from the test suite, and an interactive mode for experimenting with (all the benchmarks). The conversion to a Rust-based test runner lost the ability to just compile the tests without running them.

[brson]

Since I opened this I have never really felt the need for it. Closing.