Move everything under kotlin-native folder

I was forced to manually do update the following files, because otherwise
they would be ignored according .gitignore settings. Probably they
should be deleted from repo.

Interop/.idea/compiler.xml
Interop/.idea/gradle.xml
Interop/.idea/libraries/Gradle__org_jetbrains_kotlin_kotlin_runtime_1_0_3.xml
Interop/.idea/libraries/Gradle__org_jetbrains_kotlin_kotlin_stdlib_1_0_3.xml
Interop/.idea/modules.xml
Interop/.idea/modules/Indexer/Indexer.iml
Interop/.idea/modules/Runtime/Runtime.iml
Interop/.idea/modules/StubGenerator/StubGenerator.iml
backend.native/backend.native.iml
backend.native/bc.frontend/bc.frontend.iml
backend.native/cli.bc/cli.bc.iml
backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2Native.kt
backend.native/cli.bc/src/org/jetbrains/kotlin/cli/bc/K2NativeCompilerArguments.kt
backend.native/tests/link/lib/foo.kt
backend.native/tests/link/lib/foo2.kt
backend.native/tests/teamcity-test.property

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

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+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
+
+@Test fun runTest() {
+    if (square(2)             != 4)   throw Error()
+    if (sumOfSquares(2, 4)    != 20)  throw Error()
+    if (diffOfSquares(2, 4)   != -12) throw Error()
+    if (mod(5, 2)             != 2)   throw Error()
+    if (remainder(5, 2)       != 1)   throw Error()
+}