[libclang] Introduce clang_Cursor_isDynamicCall which,

given a cursor pointing to a C++ method call or an ObjC message,
returns non-zero if the method/message is "dynamic", meaning:

  For a C++ method: the call is virtual.
  For an ObjC message: the receiver is an object instance, not 'super' or a
  specific class.

rdar://11779185

llvm-svn: 159627