tools/fast: fix unused var, use Stopwatch, .gitignore

cmd/tools/fast/.gitignore

@@ -1,3 +1,5 @@
 fast
-v2
 index.html
+table.html
+v.c
+v2

cmd/tools/fast/fast.v

@@ -76,11 +76,11 @@ fn exec(s string) string {
 // returns milliseconds
 fn measure(cmd string) int {
 	println('Warming up...')
-	for i in 0..3 {
+	for _ in 0..3 {
 		exec(cmd)
 	}
 	println('Building...')
-	ticks := time.ticks()
+	sw := time.new_stopwatch()
 	exec(cmd)
-	return int(time.ticks() - ticks)
+	return int(sw.elapsed().milliseconds())
 }