Add support for CallExpr::isBuiltinConstantExpr(). For now, this hook is used to support CFConstantStrings. Can be extended to support other built-in functions.

This allows the following code to compile without error...

#include <CoreFoundation/CoreFoundation.h>

#define CONST_STRING_DECL(S, V) const CFStringRef S = (const CFStringRef)__builtin___CFStringMakeConstantString(V);

CONST_STRING_DECL(kCFTimeZoneSystemTimeZoneDidChangeNotification, "kCFTimeZoneSystemTimeZoneDidChangeNotification")

llvm-svn: 46592