msys native python testsuite support doesn't work in some situations

On a vanilla Windows 8.1, msys2 GHC installation with only msys python installed, the testsuite driver is broken. I know of one other person whose testsuite is also not working. The usual error message is:

cd ./typecheck/should_compile &&  "C:/msys64/home/ezy.exe" -c tc055.hs -fforce-recomp -dcore-lint -dcmm-lib -rtsopts -fno-warn-tabs -fno-ghci-history -fno-warnrr 2>&1
'..\timeout\install-inplace\bin\timeout.exe" "300" "cexternal command,
operable program or batch file.
Compile failed (status 256) errors were:

I have diagnosed the problem to the fact that we are passing a complex command string to cmd with adequately quoting it. In particular, when I inspect the command line that Python is attempting to invoke, it looks something like this:

cmd \c 'timeout.exe 300 "cd . && "inplace/ghc-stage2" -c blah blah"'

Notice, in particular, that the quoted GHC executable was not inside the timeout invocation is not double-quoted, so cmd does NOT parse the command the way you want it to.

Curiously enough, when I remove this fix (introduced by commit 101c62e26286353dd3fac1ef54323529b64c9902), the msys Python runner works fine. So I don't even know what this commit was intended to fix; it seems to have done more harm than good

Here are some details about my configuration:

ezyang@cutlass MSYS ~/ghc-validate/testsuite
$ python2 --version
Python 2.7.9

ezyang@cutlass MSYS ~/ghc-validate/testsuite
$ bash --version
GNU bash, version 4.3.33(3)-release (x86_64-pc-msys)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

Trac metadata

Trac field	Value
Version	7.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Test Suite
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