openmp: Fix ICE on depend(source) clause during cdtor cloning [PR100957]

openmp: Fix ICE on depend(source) clause during cdtor cloning [PR100957]

The depend(source) clause has NULL OMP_CLAUSE_DECL, it has just the
depend kind specified and no arguments.  So copy_tree_body_r shouldn't
check TREE_CODE on it without checking it is non-NULL.

2021-06-08  Jakub Jelinek  <jakub@redhat.com>

	PR c++/100957
	* tree-inline.c (copy_tree_body_r): For OMP_CLAUSE_DEPEND don't
	check TREE_CODE if OMP_CLAUSE_DECL is NULL.

	* g++.dg/gomp/doacross-2.C: New test.