Windows: downgrade MinGW version to work around CGO issue

see golang/go#51007
see docker#293 (comment)

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

dockerfiles/win.dockerfile

@@ -18,6 +18,9 @@ ARG GO111MODULE=auto
 ENV GO111MODULE=$GO111MODULE \
  chocolateyUseWindowsCompression=false
 # Install make and gcc
+# We install an older version of MinGW to workaround issues in CGO;
+# see https://github.com/golang/go/issues/51007
 RUN iex ((new-object net.webclient).DownloadString('https://chocolatey.org/install.ps1')); \
  choco feature disable --name showDownloadProgress; \
- choco install -y make mingw
+ choco install -y make; \
+ choco install -y mingw --version 10.2.0 --allow-downgrade