Replace POP with ARETURN if it pops Unit and ARETURN shall return Unit

#KT-16880: Fixed

compiler/testData/codegen/bytecodeListing/tailSuspendUnitFun.kt

@@ -0,0 +1,61 @@
+suspend fun empty() {}
+suspend fun withoutReturn() { empty() }
+suspend fun withReturn() { return empty() }
+suspend fun notTailCall() { empty(); empty() }
+suspend fun lambdaAsParameter(c: suspend ()->Unit) { c() }
+suspend fun lambdaAsParameterNotTailCall(c: suspend ()->Unit) { c(); c() }
+suspend fun lambdaAsParameterReturn(c: suspend ()->Unit) { return c() }
+suspend fun returnsInt() = 42
+// This should not be tail-call, since the caller should push Unit.INSTANCE on stack
+suspend fun callsIntNotTailCall() { returnsInt() }
+suspend fun multipleExitPoints(b: Boolean) { if (b) empty() else withoutReturn() }
+suspend fun multipleExitPointsNotTailCall(b: Boolean) { if (b) empty() else returnsInt() }
+
+fun ordinary() = 1
+inline fun ordinaryInline() { ordinary() }
+suspend fun multipleExitPointsWithOrdinaryInline(b: Boolean) { if (b) empty() else ordinaryInline() }
+
+suspend fun multipleExitPointsWhen(i: Int) {
+    when(i) {
+        1 -> empty()
+        2 -> withReturn()
+        3 -> withoutReturn()
+        else -> lambdaAsParameter {}
+    }
+}
+
+suspend fun <T> generic(): T = TODO()
+suspend fun useGenericReturningUnit() {
+    generic<Unit>()
+}
+
+class Generic<T> {
+    suspend fun foo(): T = TODO()
+}
+suspend fun useGenericClass(g: Generic<Unit>) {
+    g.foo()
+}
+
+suspend fun <T> genericInferType(c: () -> T): T = TODO()
+suspend fun useGenericIngerType() {
+    genericInferType {}
+}
+
+suspend fun nullableUnit(): Unit? = null
+suspend fun useNullableUnit() {
+    nullableUnit()
+}
+
+suspend fun useRunRunRunRunRun() {
+    run {
+        run {
+            run {
+                run {
+                    run {
+                        empty()
+                    }
+                }
+            }
+        }
+    }
+}