Fix temporary paths in both MSYS and MSYS2.

* /home/Renato/AppData/Local/Temp isn't actually exported from /etc/profile in MSYS2, switching to C:\Users\Renato\AppData\Local\Temp.
* MSYS actually does define MINGW32, so we now rely on the absence of C:\Users\Renato\AppData\Local\Temp for identifying it (hopefully this is cheaper than checking the version with 2.0.0(0.273/5/3)).