Added the ability to create an objective C method for an objective C

interface in ClangASTContext. Also added two bool returning functions that
indicated if an opaque clang qual type is a CXX class type, and if it is an
ObjC class type.

Objective C classes now will get their methods added lazily as they are
encountered. The reason for this is currently, unlike C++, the 
DW_TAG_structure_type and owns the ivars, doesn't not also contain the
member functions. This means when we parse the objective C class interface
we either need to find all functions whose names start with "+[CLASS_NAME"
or "-[CLASS_NAME" and add them all to the class, or when we parse each objective
C function, we slowly add it to the class interface definition. Since objective
C's class doesn't change internal bits according to whether it has certain types
of member functions (like C++ does if it has virtual functions, or if it has
user ctors/dtors), I currently chose to lazily populate the class when each
functions is parsed. Another issue we run into with ObjC method declarations
is the "self" and "_cmd" implicit args are not marked as artificial in the
DWARF (DW_AT_artifical), so we currently have to look for the parameters by
name if we are trying to omit artificial function args if the language of the
compile unit is ObjC or ObjC++.

llvm-svn: 114722