Constify wrap_here/wrap_hint code path

Constify wrap_here/wrap_hint code path

Constify the data path between ui_out_wrap_hint and the wrap_indent
global, because we can.  It's clearer that the argument passed to
wrap_hint is not intended to be modified by the ui_out implementation.

gdb/ChangeLog:

	* mi/mi-out.c (mi_wrap_hint): Constify argument.
	* cli-out.c (cli_wrap_hint): Likewise.
	* ui-out.c (ui_out_wrap_hint, uo_wrap_hint): Likewise.
	* ui-out.h (ui_out_wrap_hint, wrap_hint_ftype): Likewise.
	* utils.c (wrap_here): Likewise.
	(wrap_indent): Constify.
	* utils.h (wrap_here): Constify argument.