fix: add flag to disable the osdeps override warnings

It's a common usage pattern, and `autoproj show` allows to see it.

lib/autoproj/configuration.rb

@@ -370,6 +370,28 @@ def prefix_dir=(path)
             set("prefix", path, true)
         end
 
+        # Whether Autoproj should warn if a package set overrides the osdep of
+        # another
+        #
+        # It is true for historical reasons. Set this to false in your
+        # workspace's init.rb for the new behavior
+        #
+        # @see osdeps_warn_overrides=
+        def osdeps_warn_overrides?
+            get "osdeps_warn_overrides", true
+        end
+
+        # Sets whether Autoproj should warn if a package set overrides the osdep
+        # of another
+        #
+        # It is true for historical reasons. Set this to false in your
+        # workspace's init.rb for the new behavior
+        #
+        # @see osdeps_warn_overrides?
+        def osdeps_warn_overrides=(flag)
+            set "osdeps_warn_overrides", flag
+        end
+
         # The directory in which packages will be installed.
         #
         # If it is a relative path, it is relative to the root dir of the

lib/autoproj/os_package_resolver.rb

@@ -210,7 +210,9 @@ def invalidate_resolve_package_cache
         # takes precedence
         def merge(info, suffixes: [])
             @definitions = definitions.merge(info.definitions) do |h, v1, v2|
-                warn_about_merge_collisions(info, suffixes, h, v1, v2) if v1 != v2
+                if v1 != v2 && ws.config.osdeps_warn_overrides?
+                    warn_about_merge_collisions(info, suffixes, h, v1, v2)
+                end
                 v2
             end
             invalidate_resolve_package_cache