[libclang] Fix cursors for arguments of Subscript and Call operators

The DeclRefExpr of CXXOperatorCallExpr refering to the custom operator
is visited before the arguments to the operator call. For the Call and
Subscript operator the range of this DeclRefExpr includes the whole call
expression, so that all tokens in that range were mapped to the operator
function, even the tokens of the arguments.

Fix this by ensuring that this particular DeclRefExpr is visited last.

Fixes PR25775.

Fix by Nikolai Kosjar.

Differential Revision: https://reviews.llvm.org/D40481

llvm-svn: 340521