scons: Also print a deprecation warning on windows

This warning is different. Meson support for windows is less mature than
for other platforms, and the goal here is to alert people that
eventually we plan to drop scons and move to meson, and that they should
try out meson and report issues.

Reviewed-by: Eric Anholt <eric@anholt.net>

SConstruct

@@ -81,6 +81,13 @@ if common.host_platform != 'windows':
               "please use meson instead. If you really need to use scons you "
               "can add `force_scons=1` to the scons command line.", file=sys.stderr)
         sys.exit(1)
+else:
+    print("WARNING: Scons support is in the process of being deprecated on "
+          "on windows platforms (including mingw). If you haven't already "
+          "please try using meson for windows builds. Be sure to report any "
+          "issues you run into", file=sys.stderr)
+
+
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 # Environment setup