Constify argv, fix warnings. (#1242)

Constify argv, fix warnings. (#1242)

* Fix perl warnings

 - cast POPs to void to avoid unused value warning
 - declare functions that don't set RETVAL as returning void

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
* Constify argv

rrd has no business modifying the string pointed to by passed agrv, and
as far as gcc can see it does indeed not modify them because it compiles
with const argv.

This fixes warnings when passing const strings into rrd, and avoids the
need to duplicate all strings in the tcl bindings.

This fixes warnings like these:
[    3s] prog/sensord/rrd.c: In function 'rrdInit':
[    3s] prog/sensord/rrd.c:302:40: warning: cast discards 'const' qualifier from pointer target type [-Wcast-qual]
[    3s]   302 |                 ret = rrd_create(argc, (char**) argv);
[    3s]       |                                        ^
[    3s] prog/sensord/rrd.c: In function 'rrdUpdate':
[    3s] prog/sensord/rrd.c:458:42: warning: cast discards 'const' qualifier from pointer target type [-Wcast-qual]
[    3s]   458 |                 if ((ret = rrd_update(3, (char **) /* WEAK */ argv))) {
[    3s]       |                                          ^

Signed-off-by: Michal Suchanek <msuchanek@suse.de>
* tcl: Do not duplicate const strings

---------

Signed-off-by: Michal Suchanek <msuchanek@suse.de>