c++/modules: Always mark tinfo vars as TREE_ADDRESSABLE [PR120350]

c++/modules: Always mark tinfo vars as TREE_ADDRESSABLE [PR120350]

We need to mark type info decls as addressable if we take them by
reference; this is done by walking the declaration during parsing and
marking the decl as needed.

However, with modules we don't stream tinfo decls directly; rather we
stream just their name and type and reconstruct them in the importer
directly.  This means that any addressable flags are not propagated, and
we error because TREE_ADDRESSABLE is not set despite taking its address.

But tinfo decls should always have TREE_ADDRESSABLE set, as any attempt
to use the tinfo decl will go through build_address anyway.  So this
patch fixes the issue by eagerly marking the constructed decl as
TREE_ADDRESSABLE so that modules gets this flag correctly set as well.

	PR c++/120350

gcc/cp/ChangeLog:

	* rtti.cc (get_tinfo_decl_direct): Mark TREE_ADDRESSABLE.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/tinfo-3_a.H: New test.
	* g++.dg/modules/tinfo-3_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 9a6e5a437f0416627ee516f6ef5929cb30c5e498)