Test command lines munged on Windows when running on msys Python

On Windows, the test runner works fine if run under Windows-native Python, but fails with the msys Python because of the heuristic transformations that msys applies to all binary invocations of non-msys binaries (such as timeout.exe) by msys binaries (such as python). This is relatively easy to sidestep by going through /usr/bin/cmd in msys which sidesteps the argument munging.

Trac metadata

Trac field	Value
Version	7.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Build System
Test case
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