Make #Pathname a module_function of Kernel like on MRI

Author: eregon

lib/truffle/pathname.rb

@@ -1072,5 +1072,5 @@ def Pathname(path) # :doc:
     return path if Primitive.class_of(path) == Pathname
     Pathname.new(path)
   end
-  private :Pathname # Truffle: private as in MRI
+  module_function :Pathname
 end