Support "-Xno-check-impl" argument, check only real declarations

Use "-Xno-check-impl" to suppress checking whether the platform declaration
implementation has the "impl" modifier.

Do not check presence of fake overrides from platform class in the impl class,
otherwise there would be a lot of errors about the fact that
equals/hashCode/toString are not marked with the "impl" modifier

compiler/tests/org/jetbrains/kotlin/multiplatform/MultiPlatformIntegrationTestGenerated.java

@@ -98,6 +98,12 @@ public class MultiPlatformIntegrationTestGenerated extends AbstractMultiPlatform
             doTest(fileName);
         }
 
+        @TestMetadata("fakeOverrides")
+        public void testFakeOverrides() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/multiplatform/classScopes/fakeOverrides/");
+            doTest(fileName);
+        }
+
         @TestMetadata("functionIncorrectSignature")
         public void testFunctionIncorrectSignature() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/multiplatform/classScopes/functionIncorrectSignature/");