Bug#1082699: tint2 FTBFS - undefined reference

[Rebecca N. Palmer]

Control: tags -1 patch

That symbol is in libm, which main tint2 is linked against but tint2conf 
isn't.  (Possibly one of its other dependencies used to pull it in and 
no longer does.)

Fix:
https://salsa.debian.org/debian/tint2/-/merge_requests/3