Rollup merge of #146601 - Enselic:fix-test-args, r=Mark-Simulacrum

compiletest: Make `./x test --test-args ...` work again

It accidentally broke with  rust-lang/rust#146501. The intention of that PR was to keep existing behavior if `--exact` is not used, but it had a bug. This PR fixes that bug.

Author: Zalathar