Add support for any location description in CFI

Add support for any location description in CFI

One of the main benefits of allowing location description to be on the
DWARF stack is that now CFI expression based register rules can be
defined using a location description operations. This allows a register
of one frame to be saved in any location, including any composite
location.

To fully support this feature, the execute_stack_op function in
dwarf2/frame.c needs to return a single struct value object instead of
just an address.

Function put_frame_register_bytes also needs to change to support any
location description.

This support is a one of the key features to truly support optimized
code.

gdb/ChangeLog:

	* dwarf2/frame.c (execute_stack_op): Change to return a struct
	value object.
	(dwarf2_frame_cache): Change to call new execute_stack_op
	definition.
	(dwarf2_frame_prev_register): Change to call new execute_stack_op
	definition.
	* frame.c (put_frame_register_bytes): Add support for writing to
	composite location description.

Change-Id: I0c23ba56310174a2f8e539be72a11ac554efcaca