Add _PTR WX_DECLARE_HASH_SET variants to fix warnings about operator->().

Add _PTR WX_DECLARE_HASH_SET variants to fix warnings about operator->().

Macros from WX_DECLARE_HASH_SET family could declare an operator->() which
could never be called because it returned a pointer to a non-object (e.g. a
pointer or a primitive type).

Fix this in the same way as for WX_DECLARE_ARRAY macros by adding (badly but
consistently) named _PTR variants of the macros to allow defining the versions
without operator->().

This fixes tons of warnings when building wx with Sun CC.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69568 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775