Clang has existing support for debuggers that

want to provide "po"-like functionality which
treats the result of an expression implicitly as
"id" (if it is not otherwise known) and prints
it as an Objective-C object.

This has in the past been gated by the
"DebuggerSupport" language option, but that is
too general.  Debuggers also provide other commands
like "print" that do not make any assumptions
about whether the object is an Objective-C object.

This patch makes the assumption conditional on a
new language option: DebuggerCastResultToId.  I
have also made corresponding modifications to the
testsuite.

llvm-svn: 149735