Cirrus CI: OK, install msys2 from Chocolatey.

I have no idea what the hell comes in the container by default, but sh
appears to be from Git.  We need something closr to a UN*X environment
than that if we're going to use the build scripts on Windows.

Author: guyharris

.cirrus.yml

@@ -70,16 +70,14 @@ windows_task:
     - choco install --no-progress -y winflexbison
     - win_flex --version
     - win_bison --version
+    - choco install -y --no-progress msys2
     - choco install --no-progress -y curl
     - curl -O -s https://www.winpcap.org/install/bin/WpdPack_4_1_2.zip
     - 7z x .\WpdPack_4_1_2.zip -oc:\projects\libpcap\Win32
     - curl -O -s https://npcap.com/dist/npcap-sdk-1.13.zip
     - 7z x .\npcap-sdk-1.13.zip -oc:\projects\libpcap\Win32\npcap-sdk
     - curl -o AirPcap_Devpack.zip -L -s "https://support.riverbed.com/bin/support/download?sid=l3vk3eu649usgu3rj60uncjqqu"
     - 7z x .\AirPcap_Devpack.zip -oc:\projects\libpcap\Win32
-    - dir/a/s C:\sh.exe
-    - sh -c "which sh`
-    - sh -c "pacman -S bc"
   env:
     MAKE_BIN: msbuild
     MAKEFLAGS: '/m /nologo /m /nologo /p:Configuration=Release'