testing/check_software: add libanl in system libraries whitelist

libanl is part of glibc since 2001 (see
https://sourceware.org/git/?p=glibc.git;a=blob;f=ChangeLog.old/ChangeLog.12;h=adcf9081d44c06e03c3899612afba7c8c0d9b3fa;hb=HEAD#l5595)

See merge request !291
Status Job ID Name Coverage
  External
failed SlapOS-Master.UnitTest-Master

12:34:34

passed SlapOS.Eggs.UnitTest-Master.Python2

01:11:17

passed SlapOS.Eggs.UnitTest-Master.Python3

00:27:47

failed SlapOS-Master.UnitTest-Master

01:06:48

passed SlapOS.Eggs.UnitTest-Master.Python2

00:07:27

passed SlapOS.Eggs.UnitTest-Master.Python2

00:55:56

passed SlapOS.Eggs.UnitTest-Master.Python3

00:08:15

passed SlapOS.Eggs.UnitTest-Master.Python3

01:56:41