[Bug libstdc++/87872] debug list::splice should not call _M_transfer_from_if on self-splices

[jbytheway at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87872

--- Comment #3 from John Bytheway <jbytheway at gmail dot com> ---
Created attachment 44955
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44955&action=edit
Proposed patch

Sure, here's a proposed patch.  Tested in the sense that I have compiled and
run a program against the changed code, but I have not run the libstdc++ test
suite or similar.

Should affect list::splice and forward_list::splice_after with _GLIBCXX_DEBUG
set.