d: Move generation of array bounds error to own function.

d: Move generation of array bounds error to own function.

gcc/d/ChangeLog:

	* d-codegen.cc (build_array_bounds_call): New function.
	(build_bounds_condition): Use build_array_bounds_call.
	* d-lang.cc (d_init_options): Explicitly set default check action to
	CHECKACTION_D.
	(d_post_options): Set check action to CHECKACTION_C if the flag
	-fno-druntime was seen.
	* d-tree.h (build_array_bounds_call): Declare.
	* expr.cc (ExprVisitor::visit (AssertExp *)): Use
	build_array_bounds_call.