lang/gnu-apl: unbreak the build on recent -CURRENT (clang 13.0.0)
Bif_F12_FORMAT.cc:579:5: error: variable 'sum' set but not used
[-Werror,-Wunused-but-set-variable]
int sum = 0;
^
1 error generated.Obtained from: upstream SVN r1498
Reported by: pkg-fallout