Core DR 342
PR c++/48582
* pt.c (check_valid_ptrmem_cst_expr): A null member pointer value
is valid in C++11.
(convert_nontype_argument): Likewise. Implicitly convert nullptr
and do constant folding.
* mangle.c (write_template_arg_literal): Mangle null member
pointer values as 0.
* call.c (null_member_pointer_value_p): New.
* cp-tree.h: Declare it.
From-SVN: r178144
