Convert DWARF expr functions to methods

Convert DWARF expr functions to methods

This converts various DWARF expr functions to be members on
dwarf_expr_context, then fixes up the various users.  This results in
somewhat less wordy code and sets the stage for the next patch.

2016-10-21  Tom Tromey  <tom@tromey.com>

	* dwarf2loc.c (per_cu_dwarf_call)
	(dwarf_expr_push_dwarf_reg_entry_value)
	(dwarf2_evaluate_loc_desc_full, dwarf2_locexpr_baton_eval)
	(needs_dwarf_reg_entry_value)
	(dwarf2_loc_desc_get_symbol_read_needs): Update.
	* dwarf2expr.h (dwarf_expr_context) <push_address, eval, fetch,
	fetch_address, fetch_in_stack_memory, address_type, grow_stack,
	push, stack_empty_p, add_piece, get_base_type, execute_stack_op,
	pop>: New method declarations.
	(dwarf_expr_push_address, dwarf_expr_eval, dwarf_expr_fetch)
	(dwarf_expr_fetch_address, dwarf_expr_fetch_in_stack_memory):
	Don't declare.
	* dwarf2expr.c (address_type, grow_stack, push, push_address)
	(pop, fetch, fetch_address, fetch_in_stack_memory)
	(stack_empty_p, add_piece, eval, get_base_type)
	(execute_stack_op): Rename.  Turn into methods.
	* dwarf2-frame.c (execute_stack_op): Update.