Prefer system gem path when deps exist

Author: hsbt

spec/bundler/support/path.rb

@@ -321,7 +321,9 @@ def sinatra_dependency_paths
         logger
         compact_index
       ]
-      path = if ruby_core? && deps.all? {|dep| !Dir[source_root.join(".bundle/gems/#{dep}-*")].empty? }
+      path = if deps.all? {|dep| !Dir[scoped_base_system_gem_path.join("gems/#{dep}-*")].empty? }
+        scoped_base_system_gem_path
+      elsif ruby_core? && deps.all? {|dep| !Dir[source_root.join(".bundle/gems/#{dep}-*")].empty? }
         source_root.join(".bundle")
       else
         scoped_base_system_gem_path