[Bug libstdc++/91871] iterator_to_const_iterator() in testsuite_hooks.h causes valid -Wreturn-stack-address warnings with LLVM

[brooks at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91871

--- Comment #1 from Brooks Moses <brooks at gcc dot gnu.org> ---
FWIW, this function only seems to be used in the seven
testsuite/23_containers/*/14340.cc tests.