c: detect variably-modified types [PR117145,PR117245,PR100420]

c: detect variably-modified types [PR117145,PR117245,PR100420]

This fixes two cases where variably-modified types were not recognized as
such.  The first is when building composite types and the other when a type
is reconstructed for the 'vector' attribute.  Construction of types in
the C FE is reorganized to use c_build_* functions which are responsible for
setting C_TYPE_VARIABLE_SIZE, C_TYPE_VARIABLY_MODIFIED and TYPE_TYPELESS_STORAGE
based on the properties of the type itself and these replace all other logic
elsewhere (e.g. in grokdeclarator).  A new 'c_reconstruct_complex_type' based
on these functions is introduced which is called via a language hook when the
'vector' attribute is processed (as for C++).

One problem is are arrays of unspecified size 'T[*]' which were represented
identically to zero-sized arrays but with C_TYPE_VARIABLE_SIZE set.  To avoid
having to create distinct type copies for this, the representation was changed
to make it a natural VLA by giving it an upper bound of '(0, 0)'.  This also
then allows fixing of PR100420 where such arrays were printed as 'T[0]'.

Finally, a new function 'c_verify_type' checks consistency of properties
specific to C FE and is called when checking is on.

	PR c/117145
	PR c/117245
	PR c/100420

gcc/c/ChangeLog:
	* c-decl.cc (c_build_pointer_type): Move to c-typeck.cc
	(grokdeclarator): Simplify logic.
	(match_builtin_function_types): Adapt.
	(push_decl): Adapt.
	(implicitly_declare): Adapt.
	(c_update_type_canonical): Adapt.
	(c_make_fname_decl): Adapt.
	(start_function): Adapt.
	* c-objc-common.h: Add LANG_HOOKS_RECONSTRUCT_COMPLEX_TYPE.
	* c-tree.h: Add prototypes.
	* c-typeck.cc (c_verify_type): New function.
	(c_set_type_bits). New function.
	(c_build_pointer_type): Moved from c-decl.cc.
	(c_build_pointer_type_for_mode): New function.
	(c_build_function_type): New function.
	(c_build_array_type): New function.
	(c_build_type_attribute_variant): New function.
	(c_reconstruct_complex_type): New function.
	(c_build_functype_attribute_variant): Renamed.
	(array_to_pointer_conversion): Simplify logic.
	(composite_type_internal): Simplify logic..
	(build_unary_op): Simplify logic..
	(comptypes_verify): Add checking assertions.
	(c_build_qualified_type): Add checking assertions.
	(c_build_function_call_vec): Adapt.
	(qualify_type): Adapt.
	(build_functype_attribute_variant): Adapt.
	(common_pointer_type): Adapt.
	(c_common_type): Adapt.
	(convert_for_assignment): Adapt.
	(type_or_builtin_type): Adapt.
	(build_access_with_size_for_counted_by): Adapt.
	(build_conditional_expr): Adapt.
	(build_modify_expr): Adapt.
	(build_binary_op): Adapt.
	(build_omp_array_section): Adapt.
	(handle_omp_array_sections): Adapt.
	(c_finish_omp_clauses): Adapt.
	* c-parser.cc (c_parser_typeof_specifier): Adapt.
	(c_parser_generic_selection): Adapt.

gcc/c-family/ChangeLog:
	* c-pretty-print.cc (c_pretty_printer::direct_abstract_declarator):
	Detect arrays of unspecified size.

gcc/testsuite/ChangeLog:
	* gcc.dg/c23-tag-composite-11.c: New test.
	* gcc.dg/Warray-parameter-4.c: Resolve xfails.
	* gcc.dg/Wvla-parameter-2.c: Resolve xfails.
	* gcc.dg/Wvla-parameter-3.c: Resolve xfails.
	* gcc.dg/pr117145-1.c: New test.
	* gcc.dg/pr117145-2.c: New test.
	* gcc.dg/pr117245.c: New test.