c++: Fix GC with TU_LOCAL_ENTITY [PR119564]

c++: Fix GC with TU_LOCAL_ENTITY [PR119564]

When adding TU_LOCAL_ENTITY in r15-6379 I neglected to add it to
cp_tree_node_structure, so garbage collection was crashing on it.

	PR c++/119564

gcc/cp/ChangeLog:

	* decl.cc (cp_tree_node_structure): Add TU_LOCAL_ENTITY; fix
	formatting.

gcc/testsuite/ChangeLog:

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

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>