stor-layout.c (layout_type): Do not clear TREE_OVERFLOW on overflowed zeroes, except in one specific case.

	* stor-layout.c (layout_type) <ARRAY_TYPE>: Do not clear TREE_OVERFLOW
	on overflowed zeroes, except in one specific case.
ada/
	* gcc-interface/decl.c (gnat_to_gnu_entity) <object>: Use
	valid_constant_size_p to detect too large objects.
	<E_Subprogram_Type>: Likewise for too large return types.
	(allocatable_size_p): Call valid_constant_size_p in the fixed case.
	(annotate_value) <INTEGER_CST>: Simplify.
	<BIT_AND_EXPR>: Deal with negative values here.
	* gcc-interface/trans.c (gnat_to_gnu) <N_Assignment_Statement>: Use
	valid_constant_size_p to detect too large objects on the LHS.
	* gcc-interface/misc.c (default_pass_by_ref): Likewise for large types.
	And use TYPE_SIZE_UNIT throughout.
	(must_pass_by_ref): Likewise.
	* gcc-interface/utils.c (max_size) <tcc_unary>: Split from common case.
	<tcc_binary>: Likewise.  Call size_binop instead of fold_build2.
	<tcc_expression>: Simplify.
	* gcc-interface/utils2.c (build_allocator): Use valid_constant_size_p
	to detect too large allocations.

From-SVN: r193886