Class-fy dwarf2_frame_state

Class-fy dwarf2_frame_state

This patch adds ctor and dtor to dwarf2_frame_state, so that we can
remove one cleanup "old_chain".

gdb:

2017-08-11  Yao Qi  <yao.qi@linaro.org>

	* dwarf2-frame.c (dwarf2_frame_state_free): Remove.
	(dwarf2_frame_state::dwarf2_frame_state): New.
	(dwarf2_frame_state::~dwarf2_frame_state): New.
	(dwarf2_fetch_cfa_info): Update.
	(dwarf2_frame_cache): Remove old_chain.  Change 'fs' to an object
	rather than a pointer.  Update code.
	* dwarf2-frame.h (struct dwarf2_frame_state): Declare ctor and
	dtor.
	<data_align, code_align, retaddr_column>: Change them to const.
	<armcc_cfa_offsets_sf, armcc_cfa_offsets_reversed>: Change them
	to bool.