Revert "The test runner now also works under the msys-native Python."
To make the test runner work under msys-native Python... Commit 5258566e broke the msys testsuite driver (#10441). It changed the quoting of `config.compiler` from single quotes to double quote, which turns out to not be compatible with what the function `passThroughCmd` expected. We could fix `passThroughCmd` to handle the case where `config.compiler` is double quoted, and scatter some notes around to make sure the quoting done in various places of the testsuite driver stay compatible. Instead, this commit reverts 101c62e2, which introdced the function `passThroughCmd` in the first place (#9626). ezyang reports that doing this revert fixes the testsuite driver for him using the the following version of msys2: msys2-keyring r8.3864337-1 msys2-runtime 18.104.22.16851.cd3184b-1 msys2-runtime-devel 22.214.171.12451.cd3184b-1 msys2-w32api-headers 126.96.36.19956.c8b6742-1 msys2-w32api-runtime 188.8.131.5255.32db221-1 Ideally we'd know what minimum version of msys2 we require, but for now this fix is better than nothing. Only gintas ever reported the original problem, and he actually mentioned shortly afterwards: "This may have been fixed by a recent release of msys2, but I am not sure." Differential Revision: https://phabricator.haskell.org/D952