Generate properly mangled test names

[Manishearth]

Currently bindgen generates a lot of tests like so:

    #[test]
    fn __bindgen_test_layout_nsTArray_instantiation_34() {
        assert_eq!(::std::mem::size_of::<root::nsTArray<root::nsCString>>() ,
                   8usize , concat ! (
                   "Size of template specialization: " , stringify ! (
                   root::nsTArray<root::nsCString> ) ));
        assert_eq!(::std::mem::align_of::<root::nsTArray<root::nsCString>>() ,
                   8usize , concat ! (
                   "Alignment of template specialization: " , stringify ! (
                   root::nsTArray<root::nsCString> ) ));
    }

The number is there because there is such a test for each T that is used as nsTArray<T>. Furthermore, the counting is global -- adding another instantiation will renumber all such tests, not just the array ones. This means that nontrivial binding updates are very prone to bitrot.

Instead of numbering this we should do something like fn __bindgen_test_layout_nsTArray_lt_nsCString_gt_instantiation. Basically, some mangling scheme that can reliably produce unique names.

cc @emilio

[fitzgen]

Was this fixed in #829 ? @Manishearth @emilio

[Manishearth]

Lol yeah looks like I filed this is twice