Improve opt_set (etc.) used for tests

buildroot/bin/pins_set

@@ -7,5 +7,5 @@ PIN=$2
 VAL=$3
 
 SED=$(which gsed || which sed)
-eval "${SED} -i '/\(\/\/\)*\(#define \+${PIN}\b\).*$/{s//\2 ${VAL}/;h};\${x;/./{x;q0};x;q9}' Marlin/src/pins/$DIR/pins_${NAM}.h" ||
+eval "${SED} -i '/^[[:blank:]]*\(\/\/\)*[[:blank:]]*\(#define \+${PIN}\b\).*$/{s//\2 ${VAL}/;h};\${x;/./{x;q0};x;q9}' Marlin/src/pins/$DIR/pins_${NAM}.h" ||
 (echo "ERROR: pins_set Can't find ${PIN}" >&2 && exit 9)