Kovri: fix environment for Win/MinGW builds

[anonimal]

Effects monero-project/kovri#431, build logs here and here. A fix is currently in-progress, ticketing for housekeeping.

[danrmiller]

I added env={'MSYSTEM': "MINGW32"} and env={'MSYSTEM': "MINGW64"} to the respective build factories and run the make command via the mingw bash shell. Mingw32 and mingw64 builds now compile but fail on tests. See
https://build.getmonero.org/builders/kovri-all-win32/builds/12 and
https://build.getmonero.org/builders/kovri-all-win64/builds/23

I opened issue #5 to enable tracking these build config changes.

[anonimal]

I've pushed a fix for tests (not related to environment). Everything looks great so far 👍 🍻 I'll reopen this issue if needed.