Implement varargs in interop for Kotlin N (#393)

* Implement CValues.equals and .hashCode

* Add trivial test for interop varargs

* Implement varargs in interop for Kotlin N

* Compile and link runtime with libffi

* Fix few places.

backend.native/tests/interop/basics/4.kt

@@ -0,0 +1,14 @@
+import cstdio.*
+import kotlinx.cinterop.*
+
+fun main(args: Array<String>) {
+    printf("%s %s %d %d %d %lld %.1f %.1lf\n",
+            "a", "b".cstr, (-1).toByte(), 2.toShort(), 3, Long.MAX_VALUE, 0.1.toFloat(), 0.2)
+
+    memScoped {
+        val aVar = alloc<CInt32Var>()
+        val bVar = alloc<CInt32Var>()
+        val sscanfResult = sscanf("42", "%d%d", aVar.ptr, bVar.ptr)
+        printf("%d %d\n", sscanfResult, aVar.value)
+    }
+}