Change sorting_description from const to var

Since this script can be reloaded in the same scope.

Fixes issue #387.
14 jobs for dailybuild_linux-x64 in 10 minutes and 35 seconds (queued for 14 seconds)
Status Job ID Name Coverage
  Build
passed #34353
FreeBSD
jsdoor-freebsd

00:03:56

passed #34354
Linux
jsdoor-linux

00:07:02

passed #34356
FreeBSD
jsdoor-windows

00:01:52

passed #34348
FreeBSD
sbbs-freebsd

00:05:25

passed #34343
Linux
sbbs-linux

00:10:30

passed #34346
Windows
sbbs-windows

00:04:53

passed #34355
FreeBSD
sexpots-freebsd

00:00:12

passed #34344
Linux
sexpots-linux

00:00:17

passed #34347
Windows
sexpots-windows

00:00:20

passed #34351
FreeBSD
syncdraw-freebsd

00:00:23

passed #34352
Linux
syncdraw-linux

00:01:01

passed #34349
FreeBSD
syncterm-freebsd

00:00:58

passed #34345
Linux
syncterm-linux

00:03:26

passed #34350
FreeBSD
syncterm-windows

00:01:44