x.py test leaves residual files behind

[matthiaskrgr]

Running ./x.py test --skip debuginfo-lldb leaves a bunch of residual files in /tmp/ on each run

rustdoctestpqiBsk
rustdoctestoXwyLP
rustdoctest8CBFTK
rustdoctestCLk1vY
rustdoctestlMVB5z
rustdoctestbi58j1
rustdoctest3scGmu
rustdoctestY3FCPW
rustdoctestKGZY7v
rustdoctestgKgSE0
rustdoctestKL4eyN
rustdoctestGS99pq
rustdoctest1XKHuA
rustdoctest0EUbfh
rustdoctestbgoNmD
rustdoctest1fvcau
rustdoctestHzvwPo
rustdoctestytTvTj
rustdoctestelpZO0
rustdoctestSbQSJe
rustdoctestbA0L3M
rustdoctestmCzsMa

[bjorn3]

When a rustc invocation fails at the right place, it doesn't clean up it's temporary files.

[matthiaskrgr]

all the tests that were run passed and the testsuite exited successfully in this run

[bjorn3]

Some tests are testing that an error happens.