Do not warn about zero-as-null when NULL is used.

Do not warn about zero-as-null when NULL is used.

gcc/cp/

Do not warn about zero-as-null when NULL is used.
* call.c (conversion_null_warnings): Check for pointer
types converted from zero constants.
(convert_like_real): Add a warning sentinel at the end.
* tree.c (maybe_warn_zero_as_null_pointer_constant): Also
check null_node_p.

testsuite/

Do not warn about zero-as-null when NULL is used.
* g++.dg/warn/Wzero-as-null-pointer-constant-7.C: New.

From-SVN: r260973