Add synthetic flag to generated private suspend functions

Private suspend functions need to be generated as package-local, since
they are called from their continuations.
However, this means that they can be called from Java, which breaks
their private visibility.
Adding synthetic to them fixes the issue.
 #KT-17584: Fixed

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeListingTestGenerated.java

@@ -145,6 +145,12 @@ public class BytecodeListingTestGenerated extends AbstractBytecodeListingTest {
         doTest(fileName);
     }
 
+    @TestMetadata("privateSuspendFun.kt")
+    public void testPrivateSuspendFun() throws Exception {
+        String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeListing/privateSuspendFun.kt");
+        doTest(fileName);
+    }
+
     @TestMetadata("samAdapterAndInlinedOne.kt")
     public void testSamAdapterAndInlinedOne() throws Exception {
         String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeListing/samAdapterAndInlinedOne.kt");