r181627 - Avoid patching storage class for block scope thread_local variables.

[Rafael Espíndola]

> Here is a tentative fix for review: the switch on the storage class "as
> written" is replaced by calls to semantics-aware methods.
> (Note: as I said previously, I am not changing the special handling of
> SC_OpenCLWorkGroupLocal storage class.)

Please include the test in the patch.

> Enea.
>

Cheers,
Rafael