* ax-gdb.c (gen_bitfield_ref): Add EXP argument, use expression

	architecture instead of current_gdbarch.
	(gen_struct_ref): Add EXP argument, pass to get_bitfield_ref.
	(gen_expr): Pass expression to get_struct_ref.

	* symtab.h (struct symbol_ops): Add GDBARCH parameter to
	tracepoint_var_ref callback.
	* ax-gdb.c (gen_var_ref): Pass architecture to tracepoint_var_ref
	symbol operation callback.
	* dwarf2loc.c (dwarf2_tracepoint_var_ref): Add GDBARCH parameter.
	Use it instead of current_gdbarch.
	(locexpr_tracepoint_var_ref): Add GDBARCH parameter.  Pass it to
	dwarf2_tracepoint_var_ref.
	(loclist_tracepoint_var_ref): Likewise.