PR26449: Fixes for bugs in __builtin_classify_type implementation

This patch fixes the following bugs in __builtin_classify_type implementation:
1) Support for member functions and fields
2) Same behavior as GCC in C mode (specifically, return integer_type_class for
   enums and pointer_type_class for function pointers and arrays). Behavior in
   C++ mode didn't changed.

Also, it refactors the whole implementation, by replacing a sequence of
if-else-if with a couple of switches.

Differential Revision: http://reviews.llvm.org/D16846

llvm-svn: 260881