[OpenCL] Add generic AS to 'this' pointer
Address spaces are cast into generic before invoking the constructor.
Added support for a trailing Qualifiers object in FunctionProtoType.
Note: This recommits the previously reverted patch,
but now it is commited together with a fix for lldb.
Differential Revision: https://reviews.llvm.org/D54862
llvm-svn: 349019