Merge pull request #615 from takkanm/suppress-unused-variable-warning

suppress unused variable warning

Fixes #600

lib/ffi/library.rb

@@ -344,7 +344,7 @@ def attach_variable(mname, a1, a2 = nil)
       raise FFI::NotFoundError.new(cname, ffi_libraries) if address.nil? || address.null?
       if type.is_a?(Class) && type < FFI::Struct
         # If it is a global struct, just attach directly to the pointer
-        s = type.new(address)
+        s = s = type.new(address) # Assigning twice to suppress unused variable warning
         self.module_eval <<-code, __FILE__, __LINE__
           @@ffi_gvar_#{mname} = s
           def self.#{mname}