Introduce a new mangling for protocol-qualified ObjC types in C++.  This allows
to provide proper overloading, and also prevents mangling conflicts with
template arguments of protocol-qualified type.

This is a non-backward-compatible mangling change, but per discussion with
John, the benefits outweigh this cost.

Fixes <rdar://problem/14074822>.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184250 91177308-0d34-0410-b5e6-96231b3b80d8