Fix compile-fail tests on windows

[Diggsey]

Fixes #27952

[rust-highfive]

r? @nikomatsakis

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[alexcrichton]

Is there a way the error in #27952 can be reproduced locally? Our bots have been running cfail tests for quite some time, so I'm curious as to what happened to make everything go wrong

[Diggsey]

The bug is that the cfail tests pass when they shouldn't on windows: the bots don't detect it because it's too meta: there's nothing to check that the cfail tests will actually fail!

Reproducing is easy: just introduce an additional compile error to one of the cfail tests, so that now rustc outputs both errors. On linux this would cause the test to fail, because an unexpected error was detected, but on windows the additional error is ignored because it doesn't match the pattern that it thinks all errors follow.

[alexcrichton]

@bors: r+ 19dc4d0

Ah ok, thanks!

[bors]

⌛ Testing commit 19dc4d0 with merge 28ef44a...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt