[Native][tests] Introduce EXIT_CODE directive

It allows to specify the expected exit code for STANDALONE_NO_TR tests.

native/native.tests/testData/samples/standalone_notr_nonzero_exit_code.kt

@@ -0,0 +1,8 @@
+// KIND: STANDALONE_NO_TR
+// EXIT_CODE: !0
+
+import kotlin.system.exitProcess
+
+fun main() {
+    exitProcess(42)
+}

native/native.tests/testData/samples/standalone_notr_nonzero_exit_code2.kt

@@ -0,0 +1,8 @@
+// KIND: STANDALONE_NO_TR
+// EXIT_CODE: 42
+
+import kotlin.system.exitProcess
+
+fun main() {
+    exitProcess(42)
+}

native/native.tests/testData/samples/standalone_notr_zero_exit_code.kt

@@ -0,0 +1,8 @@
+// KIND: STANDALONE_NO_TR
+// EXIT_CODE: 0
+
+import kotlin.system.exitProcess
+
+fun main() {
+    exitProcess(0)
+}