devel/lace: fix build on ARM / POWER

/wrkdirs/usr/ports/devel/lace/work/lace-1.4.2/benchmarks/matmul/matmul-seq.c:118:44: error: result of comparison of constant -1 with expression of type 'char' is always true [-Werror,-Wtautological-constant-out-of-range-compare]

118 |     while ((c=getopt(argc, argv, "w:q:h")) != -1) {
    |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^  ~~

1 error generated.