var-tracking.c: Fix some comments.

var-tracking.c: Fix some comments.

	* var-tracking.c: Fix some comments.
	(frame_stack_adjust): New.
	(vt_stack_adjustments): Init stack_adjust of entry block to
	minus stack adjustment of function prologue.
	(adjust_stack_reference): Do not adjust if adjustment == 0.
	(compute_bb_dataflow): Use plus_constant instead of gen_rtx_PLUS.
	(emit_notes_in_bb): Likewise.
	(vt_add_function_parameters): Do not adjust locations of
	function arguments.
	(vt_initialize): Compute the stack adjustment of function
	prologue and offset the initial "location" of frame_base_decl
	from the stack pointer after prologue.

From-SVN: r84106