Auto merge of #1091 - RalfJung:run-test, r=RalfJung
Auto merge of #1091 - RalfJung:run-test, r=RalfJung

run-test: make sure the sysroot building output does not distort our tests

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri,tsion/miri