-Wwrite-strings: MI -info-os

-Wwrite-strings: MI -info-os

-Wwrite-strings flags this attempt to convert a string literal to
 "char *":

      info_osdata_command ("", 0);

info_osdata_command is a command function.  We could address this by
simply passing NULL instead of "".  However, I went a little bit
further and added a new function that is called by both the CLI and
MI.

gdb/ChangeLog:
2017-04-05  Pedro Alves  <palves@redhat.com>

	* mi/mi-cmd-info.c (mi_cmd_info_os): Call info_osdata instead of
	info_osdata_command.
	* osdata.c (info_osdata_command): Rename to ...
	(info_osdata): ... this.  Constify 'type' parameter, and remove
	the 'from_tty' parameter.  Accept NULL TYPE.
	(info_osdata_command): New function.
	* osdata.h (info_osdata_command): Remove declaration.
	(info_osdata): New declaration.