Generate SuspendFunction marker interface if supertype is suspend

Otherwise, is/as checks will not work.
 #KT-18707

compiler/testData/codegen/box/coroutines/featureIntersection/suspendFunctionAsSupertypeIsCheck.kt

@@ -0,0 +1,49 @@
+// WITH_RUNTIME
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND: JVM
+// !LANGUAGE: +SuspendFunctionAsSupertype
+
+import kotlin.coroutines.*
+
+class C: suspend () -> Unit {
+    override suspend fun invoke() {
+    }
+}
+
+interface I: suspend () -> Unit {}
+
+fun interface FI: suspend () -> Unit {}
+
+@Suppress("INCOMPATIBLE_TYPES")
+fun box(): String {
+    val c = C()
+    if (c !is SuspendFunction0<*>) return "FAIL 1"
+    if (c !is Function1<*, *>) return "FAIL 2"
+    if (c is SuspendFunction1<*, *>) return "FAIL 3"
+
+    val i = object : I {
+        override suspend fun invoke() {
+        }
+    }
+    if (i !is SuspendFunction0<Unit>) return "FAIL 4"
+    if (i !is Function1<*, *>) return "FAIL 5"
+    if (i is SuspendFunction1<*, *>) return "FAIL 6"
+
+    val fi = object : FI {
+        override suspend fun invoke() {
+        }
+    }
+    if (fi !is SuspendFunction0<Unit>) return "FAIL 7"
+    if (fi !is Function1<*, *>) return "FAIL 8"
+    if (fi is SuspendFunction1<*, *>) return "FAIL 9"
+
+    val o = object : suspend () -> Unit {
+        override suspend fun invoke() {
+        }
+    }
+    if (o !is SuspendFunction0<Unit>) return "FAIL 10"
+    if (o !is Function1<*, *>) return "FAIL 11"
+    if (o is SuspendFunction1<*, *>) return "FAIL 12"
+
+    return "OK"
+}