Derive the names of tests and anon structs from the name of the type

[Manishearth]

Currently we generate a lot of __bindgen_test_layout_template_9-like functions, as well as use a similar way to create anonymous structs.

We should include the type name in these names. Or put them inside a module that has a name derived from the type. Within the module we can use a counting scheme.

The problem is that a change that introduces a type midway in the file will affect all the other numbers, causing lots of churn. In a recent patch I worked around this by deleting the churn from the patch and renaming the function to __bindgen_test_layout_template_9_TEMPORARY so that it gets fixed in the next sync.