backend/tests: add interop3 (uses callback)

backend.native/tests/build.gradle

@@ -1359,6 +1359,12 @@ task interop2(type: RunInteropKonanTest) {
     interop = 'cstdio'
 }
 
+task interop3(type: RunInteropKonanTest) {
+    goldValue = "8 9 12 13 14 \n"
+    source = "interop/basics/3.kt"
+    interop = 'cstdlib'
+}
+
 task interop_echo_server(type: RunInteropKonanTest) {
     if (isLinux()) {
         disabled = true

backend.native/tests/interop/basics/3.kt

@@ -0,0 +1,29 @@
+import kotlinx.cinterop.*
+
+fun main(args: Array<String>) {
+    memScoped {
+        val count = 5
+
+        val values = allocArray<CInt32Var>(count)
+        values[0].value = 14
+        values[1].value = 12
+        values[2].value = 9
+        values[3].value = 13
+        values[4].value = 8
+
+        cstdlib.qsort(values[0].ptr, count.toLong(), CInt32Var.size, staticCFunction(::comparator))
+
+        for (i in 0 .. count - 1) {
+            print(values[i].value)
+            print(" ")
+        }
+        println()
+    }
+}
+
+private fun comparator(a: COpaquePointer?, b: COpaquePointer?): Int {
+    val aValue = a!!.reinterpret<CInt32Var>().pointed.value
+    val bValue = b!!.reinterpret<CInt32Var>().pointed.value
+
+    return (aValue - bValue)
+}