versioning: Set DEFAULT_DOCKCROSS_IMAGE based on the image tag

This ensures that the dockcross script will continue to use the specific
tagged version of the image that generates it.

windows-x64-posix/Dockerfile.in

@@ -7,15 +7,16 @@ ARG MXE_TARGET_THREAD=.posix
 
 #include "common.windows"
 
-ENV DEFAULT_DOCKCROSS_IMAGE dockcross/windows-x64-posix
-
 # Build-time metadata as defined at http://label-schema.org
 ARG BUILD_DATE
-ARG IMAGE
+ARG IMAGE=dockcross/windows-x64-posix
+ARG VERSION=latest
 ARG VCS_REF
 ARG VCS_URL
 LABEL org.label-schema.build-date=$BUILD_DATE \
       org.label-schema.name=$IMAGE \
+      org.label-schema.version=$VERSION \
       org.label-schema.vcs-ref=$VCS_REF \
       org.label-schema.vcs-url=$VCS_URL \
       org.label-schema.schema-version="1.0"
+ENV DEFAULT_DOCKCROSS_IMAGE ${IMAGE}:${VERSION}