cgraph: A COMDAT decl always has non-zero address.

cgraph: A COMDAT decl always has non-zero address.

We should be able to assume that a template instantiation or other COMDAT
has non-zero address even if MAKE_DECL_ONE_ONLY for the target sets
DECL_WEAK and we haven't yet decided to emit a definition in this
translation unit.

gcc/ChangeLog
2020-02-26  Jason Merrill  <jason@redhat.com>

	PR c++/92003
	* symtab.c (symtab_node::nonzero_address): A DECL_COMDAT decl has
	non-zero address even if weak and not yet defined.