[Wasm] Fix SuspendFunctionKind.DELEGATING bug (KT-60700)

When detecting function delegation at the last statement position we
need to make sure that delegating call has unit return type, otherwise
we would try to return non-Unit value from a parent function returning
 Unit

^KT-60700 Fixed

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/coroutines/AbstractSuspendFunctionsLowering.kt

@@ -100,7 +100,12 @@ abstract class AbstractSuspendFunctionsLowering<C : CommonBackendContext>(val co
         // This happens a lot in practice because of suspend functions with default arguments.
         // TODO: use TailRecursionCallsCollector.
         val lastCall = when (val lastStatement = (body as IrBlockBody).statements.lastOrNull()) {
-            is IrCall -> lastStatement
+            is IrCall ->
+                // Delegation to call without return can only be performed to Unit-returning function call from Unit-returning function
+                if (lastStatement.type == context.irBuiltIns.unitType && function.returnType == context.irBuiltIns.unitType)
+                    lastStatement
+                else
+                    null
             is IrReturn -> {
                 var value: IrElement = lastStatement
                 /*

compiler/testData/codegen/box/callableReference/adaptedReferences/suspendUnitConversion.kt

@@ -12,8 +12,6 @@ suspend fun bar(): Int = suspendCoroutineUninterceptedOrReturn<Int> {
 }
 
 fun box(): String {
-    return "OK" // KT-60700 Test is hardmuted due to WASM failures on Win&Mac, but not on Linux. So, `// IGNORE_BACKEND: WASM` does not help
-
     var result = ""
     suspend {
         foo(::bar)