Working LLVM bug report link: https://bugs.llvm.org/show_bug.cgi?id=17782
C++ LWG issue: https://cplusplus.github.io/LWG/lwg-active.html#2381
(And just to show that we aren't the only ones hitting this: https://savannah.gnu.org/bugs/?47413; there is also some (closed, as they added a workaround) bug report for chromium)
(Also closed #4653 as a dupe.)