PTX: Add intrinsics to list of built-in intrinsics, which allows them to be

     used by Clang.  To help Clang integration, the PTX target has been split
     into two targets: ptx32 and ptx64, depending on the desired pointer size.

- Add GCCBuiltin class to all intrinsics
- Split PTX target into ptx32 and ptx64

llvm-svn: 129851