* dwarf2expr.h (dwarf_value_location): Add more comments describing

	* dwarf2expr.h (dwarf_value_location): Add more comments describing
	enum values.
	(struct dwarf_stack_value): New struct.
	(struct dwarf_expr_context): Change type of `stack' from CORE_ADDR*
	to struct dwarf_stack_value*.
	(struct dwarf_expr_piece): Move `v.value' into its own struct, v.expr,
	all uses updated.  Add v.expr.in_stack_memory.
	(dwarf_expr_push): Update declaration.
	(dwarf_expr_fetch_in_stack_memory): Declare.
	* dwarf2expr.c (dwarf_expr_grow_stack): Update calculation of
	size of stack value.
	(dwarf_expr_push): New arg in_stack_memory, all callers updated.
	(dwarf_expr_fetch_in_stack_memory): New function.
	(add_piece): Set in_stack_memory for non-literal values.
	(execute_stack_op): Allow ops to specify whether the value is on the
	program's stack.
	(execute_stack_op, case DW_OP_fbreg): Mark value as in stack memory.
	(execute_stack_op, case DW_OP_call_frame_cfa): Ditto.
	(execute_stack_op, case DW_OP_dup): Copy in_stack_memory flag.
	(execute_stack_op, cases DW_OP_pick, DW_OP_over): Ditto.
	(execute_stack_op, cases DW_OP_swap, DW_OP_rot): Update type of
	dwarf stack value.
	* dwarf2loc.c (read_pieced_value): Call read_stack for values known
	to be on the program's stack.
	(dwarf2_evaluate_loc_desc, case DWARF_VALUE_MEMORY): Call
	set_value_stack only for objects known to be in stack memory.
	* dwarf2-frame.c (execute_stack_op): New arg initial_in_stack_memory,
	all callers updated.