Update on format attribute handling.

- Remove the printf0 special handling as we treat it as printf anyway.
- Perform basic checks (non-literal, empty) for all formats and not only printf/scanf.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149236 91177308-0d34-0410-b5e6-96231b3b80d8