That might be sufficient for this case, but temploid friends violate an
assumption of the implementation -- namely that module A cannot create an entity
that belongs in module B's symbol table. This causes a bunch of excitement,
particularly around handling (well formed) duplicatd instantions.
Here we're not clearing DECL_UNINSTANTIATED_TEMPLATE_FRIEND_P for
the instantiated/injected template friend class B, which confuses a
later call to get_originating_module_decl for B. This patch fixes this
by clearing the flag in tsubst_friend_class (as is already done for
template friend functions
