[libclang] Make sure that when we have multiple @class references in the same line,

that later ones do not override the previous ones.

If we have:
   @class Foo, Bar;
source ranges for both start at '@', so 'Bar' will end up overriding
'Foo' even though the cursor location was at 'Foo'.

rdar://11257578

llvm-svn: 154873