Use the correct extension_safe copt for extension_safe attribute

The previous copt was in error, and was not caught due to only causing warnings to be omitted. Tests are now updated to throw an error in such cases of warning.

RELNOTES: None.
PiperOrigin-RevId: 157150798

src/main/java/com/google/devtools/build/lib/rules/objc/MultiArchSplitTransitionProvider.java

@@ -52,7 +52,7 @@ public class MultiArchSplitTransitionProvider implements SplitTransitionProvider
       "Invalid version string \"%s\". Version must be of the form 'x.y' without alphabetic "
           + "characters, such as '4.3'.";
 
-  private static final String EXTENSION_COPT = "-application-extension";
+  private static final String EXTENSION_COPT = "-fapplication-extension";
   private static final ImmutableSet<PlatformType> SUPPORTED_PLATFORM_TYPES =
       ImmutableSet.of(
           PlatformType.IOS, PlatformType.WATCHOS, PlatformType.TVOS, PlatformType.MACOS);