vup: run make only on breaking changes

cmd/tools/vup.v

@@ -43,11 +43,19 @@ fn main() {
 
 		backup('cmd/tools/vup.exe')
 	} $else {
+		self_result := os.exec('./v self') or {
+			panic(err)
+		}
+		println(self_result.output)
+		if self_result.exit_code != 0 {
+			// v self failed, have to use make
+			println('v self failed, running make...')
 			make_result := os.exec('make') or {
 				panic(err)
 			}
 			println(make_result.output)
 		}
+	}
 
 	_ := os.exec('v cmd/tools/vup.v') or {
 		panic(err)