With volatile, two 'x.data' comp refs aren't regarded as identical,
causing that the two items in the first map of
  map(to:x.a, x.a.data) map(pset: x.a.data)
end up in separate 'map(struct:x)', which will cause a later ICE.

Solution: Ignore side effects when checking the operands in the hash
for being equal. (Do so by creating a variant of tree_operand_hash
that calls operand_equal_p with OEP_MATCH_SIDE_EFFECTS.)

gcc/ChangeLog:

	PR middle-end/108545
	* gimplify.cc (struct tree_operand_hash_no_se): New.
	(omp_index_mapping_groups_1, omp_index_mapping_groups,
	omp_reindex_mapping_groups, omp_mapped_by_containing_struct,
	omp_tsort_mapping_groups_1, omp_tsort_mapping_groups,
	oacc_resolve_clause_dependencies, omp_build_struct_sibling_lists,
	gimplify_scan_omp_clauses): Use tree_operand_hash_no_se instead
	of tree_operand_hash.

gcc/testsuite/ChangeLog:

	PR middle-end/108545
	* c-c++-common/gomp/map-8.c: New test.
	* gfortran.dg/gomp/map-9.f90: New test.