Use the STRIP variable during prepend stage

A hardcoded strip does not work when cross compiling.

cook.sh

@@ -378,7 +378,7 @@ function op {
                         then
                             cp -v "$bin" "$stage/$BINDIR/$(basename $bin)"
                         else
-                            strip -v "$bin" -o "$stage/$BINDIR/$(basename $bin)"
+                            ${STRIP} -v "$bin" -o "$stage/$BINDIR/$(basename $bin)"
                         fi
                     done
                 else