rustc: Give glue symbols meaningful names

Instead of `glue_drop1234` it's `Type::<hash>::glue_drop1234`

Haven't done any performance testing.
auto merge of #6706 : brson/rust/glue, r=catamorphism

Instead of `glue_drop1234` it's `Type::<hash>::glue_drop1234`

Haven't done any performance testing.