libgcc: Move cfa_how into potential padding in struct frame_state_reg_info

libgcc: Move cfa_how into potential padding in struct frame_state_reg_info

On many architectures, there is a padding gap after the how array
member, and cfa_how can be moved there.  This reduces the size of the
struct and the amount of memory that uw_frame_state_for has to clear.

There is no measurable performance benefit from this on x86-64 (even
though the memset goes from 120 to 112 bytes), but it seems to be a
good idea to do anyway.

libgcc/

	* unwind-dw2.h (struct frame_state_reg_info): Move cfa_how member
	and reduce its size.