The frontend will attempt to not emit all template instantiations if it
thinks that the instantiation isn't used. However it sometimes get this
wrong, so you have to override it and tell it to emit them all anyway
and let the linker do the eliding instead.
This is a known problem of all the compilers since its done by the
shared frontend, rather than the glue layer.
It is a bug, but given how complex and time consuming it can be to
minimize it to a small reproducible example, its not always worth the
time to try and report it.
