Rollup merge of #48143 - nikomatsakis:termination_trait_in_tests, r=eddyb

Termination trait in tests

Support the `Termination` trait in unit tests (cc https://github.com/rust-lang/rust/issues/43301)

Also, a drive-by fix for #47075.

This is joint work with @bkchr.

diff --cc src/librustc_driver/driver.rs
Simple merge

diff --cc src/libstd/lib.rs
Simple merge

diff --cc src/libsyntax/ext/build.rs
Simple merge

diff --cc src/libsyntax/test.rs
Simple merge