[binutils-gdb] Use ui_out_emit_tuple in more places in MI

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 0092b74da6d86185c4d0c0fa0f540b97647bf44a ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 0092b74da6d86185c4d0c0fa0f540b97647bf44a

Use ui_out_emit_tuple in more places in MI

This patch changes a few more spots in MI to use ui_out_emit_tuple.
These changes required the use of gdb::optional.

ChangeLog
2017-04-22  Tom Tromey  <tom@tromey.com>

	* mi/mi-main.c (print_variable_or_computed): Use ui_out_emit_tuple.
	* mi/mi-cmd-var.c (varobj_update_one): Use ui_out_emit_tuple.
	* mi/mi-cmd-stack.c (list_arg_or_local): Use ui_out_emit_tuple.