BC native tests port to Konan's TestRunner

backend.native/tests/codegen/function/arithmetic.kt

@@ -1,10 +1,14 @@
+package codegen.function.arithmetic
+
+import kotlin.test.*
+
 fun square(a:Int):Int = a * a
 fun sumOfSquares(a:Int, b:Int):Int = square(a) + square(b)
 fun diffOfSquares(a:Int, b:Int):Int = square(a) - square(b)
 fun mod(a:Int,b:Int):Int = a / b
 fun remainder(a:Int, b:Int):Int = a % b
 
-fun main(args:Array<String>) {
+@Test fun runTest() {
     if (square(2)             != 4)   throw Error()
     if (sumOfSquares(2, 4)    != 20)  throw Error()
     if (diffOfSquares(2, 4)   != -12) throw Error()