`_fail` tests should fail if compilation fails

[vecchiot-aws]

The test at src/test/cbmc/DynTrait/main_fail.rs uses _VERIFIER_expect_fail instead of __VERIFIER_expect_fail, causing it to have a rust compile error.

I expect it went by unnoticed because we (accidentally?) left in the _fail suffix, when really it shouldn't fail, and we don't distinguish between compilation failure and verification failure.

[avanhatt]

Oh oh, we should totally distinguish between compilation and verification failures (I thought we did, unless a test was _ignore or _fixme).

[avanhatt]

Fixing this actual test in #342, but let's use this issue to track failing for _fail compilation errors?

[bdalrhm]

You're both right. We don't currently check for the kind of errors we get from tests. I happen to need this feature for the dashboard as well. So, I will make it a priority.