openmp: Fix up error recovery for invalid structured bindings in OpenMP range for...

openmp: Fix up error recovery for invalid structured bindings in OpenMP range for loops [PR105839]

The PR108503 temporary DECL_HAS_VALUE_EXPR_P clearing code can ICE
during recovery, because cp_finish_decomp when it detects errors and
reports them clears DECL_HAS_VALUE_EXPR_P, clears DECL_VALUE_EXPR and
sets TREE_TYPE of the structured binding vars to error_mark_node.
The PR108503 code had an assertion that DECL_HAS_VALUE_EXPR_P is set
so that it can clear it and restore later.

The following patch allows DECL_HAS_VALUE_EXPR_P to be unset if
type is error_mark_node and doesn't set it again in that case.

2023-03-02  Jakub Jelinek  <jakub@redhat.com>

	PR c++/105839
	* parser.cc (cp_convert_omp_range_for): Allow in assert
	decomp_first_name without DECL_HAS_VALUE_EXPR_P if it has
	error_mark_node type.
	(cp_finish_omp_range_for): Don't set DECL_HAS_VALUE_EXPR_P back
	on decls which have error_mark_node type.

	* g++.dg/gomp/pr105839-1.C: New test.
	* g++.dg/gomp/pr105839-2.C: New test.