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/cli/src/org/jetbrains/kotlin/cli/common/CLICompiler.java

@@ -281,6 +281,9 @@ public abstract class CLICompiler<A extends CommonCompilerArguments> {
         if (arguments.multiPlatform) {
             extraLanguageFeatures.add(LanguageFeature.MultiPlatformProjects);
         }
+        if (arguments.noCheckImpl) {
+            extraLanguageFeatures.add(LanguageFeature.MultiPlatformDoNotCheckImpl);
+        }
 
         configuration.put(
                 CommonConfigurationKeys.LANGUAGE_VERSION_SETTINGS,