OpenMP: Array shaping operator and strided "target update" for C

OpenMP: Array shaping operator and strided "target update" for C

Following the similar support for C++, here is the C implementation for
the OpenMP 5.0 array-shaping operator, and for strided and rectangular
updates for "target update".

Much of the implementation is shared with the C++ support added by the
previous patch.  Some details of parsing necessarily differ for C,
but the general ideas are the same.

This version of the patch has been rebased and contains a couple of
minor fixes relative to versions posted previously.

2023-09-05  Julian Brown  <julian@codesourcery.com>

gcc/c/
	* c-parser.cc (c_parser_braced_init): Disallow array-shaping operator
	in braced init.
	(c_parser_conditional_expression): Disallow array-shaping operator in
	conditional expression.
	(c_parser_cast_expression): Add array-shaping operator support.
	(c_parser_postfix_expression): Disallow array-shaping operator in
	statement expressions.
	(c_parser_postfix_expression_after_primary): Add OpenMP array section
	stride support.
	(c_parser_expr_list): Disallow array-shaping operator in expression
	lists.
	(c_array_type_nelts_top, c_array_type_nelts_total): New functions.
	(c_parser_omp_variable_list): Support array-shaping operator.
	(c_parser_omp_target_update): Recognize GOMP_MAP_TO_GRID and
	GOMP_MAP_FROM_GRID map kinds as well as OMP_CLAUSE_TO/OMP_CLAUSE_FROM.
	* c-tree.h (c_omp_array_shaping_op_p, c_omp_has_array_shape_p): New
	extern declarations.
	(create_omp_arrayshape_type): Add prototype.
	* c-typeck.cc (c_omp_array_shaping_op_p, c_omp_has_array_shape_p): New
	globals.
	(build_omp_array_section): Permit integral types, not just integer
	constants, when creating array types for array sections.
	(create_omp_arrayshape_type): New function.
	(handle_omp_array_sections_1): Add DISCONTIGUOUS parameter.  Add
	strided/rectangular array section support.
	(omp_array_section_low_bound): New function.
	(handle_omp_array_sections): Add DISCONTIGUOUS parameter.  Add
	strided/rectangular array section support.
	(c_finish_omp_clauses): Update calls to handle_omp_array_sections.
	Handle discontiguous updates.

gcc/testsuite/
	* gcc.dg/gomp/bad-array-shaping-c-1.c: New test.
	* gcc.dg/gomp/bad-array-shaping-c-2.c: New test.
	* gcc.dg/gomp/bad-array-shaping-c-3.c: New test.
	* gcc.dg/gomp/bad-array-shaping-c-4.c: New test.
	* gcc.dg/gomp/bad-array-shaping-c-5.c: New test.
	* gcc.dg/gomp/bad-array-shaping-c-6.c: New test.
	* gcc.dg/gomp/bad-array-shaping-c-7.c: New test.

libgomp/
	* testsuite/libgomp.c/array-shaping-1.c: New test.
	* testsuite/libgomp.c/array-shaping-2.c: New test.
	* testsuite/libgomp.c/array-shaping-3.c: New test.
	* testsuite/libgomp.c/array-shaping-4.c: New test.
	* testsuite/libgomp.c/array-shaping-5.c: New test.
	* testsuite/libgomp.c/array-shaping-6.c: New test.