[Sema][ObjC] Warn about 'performSelector' calls with selectors

that return record or vector types

The performSelector family of methods from Foundation use objc_msgSend to
dispatch the selector invocations to objects. However, method calls to methods
that return record types might have to use the objc_msgSend_stret as the return
value won't find into the register. This is also supported by this sentence from
performSelector documentation: "The method should not have a significant return
value and should take a single argument of type id, or no arguments". This
commit adds a new warning that warns when a selector which corresponds to a
method that returns a record type is passed into performSelector.

rdar://12056271

Differential Revision: https://reviews.llvm.org/D30174

llvm-svn: 297019