Remove enable_modules from ObjcCppSemantics

This was added as a workaround for an include validation problem on
Apple when the objc_library enable_modules attribute is set to true.
There were absolute paths to internal stl wrapper headers that were
showing up in .d files.  I verified that the absolute paths are no
longer showing up, and removing this work around didn't break any
builds.

This finally makes ObjcCppSemantics stateless which is the way it
should be!

PiperOrigin-RevId: 368850814

src/main/java/com/google/devtools/build/lib/rules/cpp/ObjcCppSemantics.java

@@ -28,19 +28,9 @@
  * CppSemantics for objc builds.
  */
 public class ObjcCppSemantics implements CppSemantics {
-  public static final ObjcCppSemantics MODULES = new ObjcCppSemantics(true);
-  public static final ObjcCppSemantics NO_MODULES = new ObjcCppSemantics(false);
+  public static final ObjcCppSemantics INSTANCE = new ObjcCppSemantics();
 
-  private final boolean enableModules;
-
-  /**
-   * Creates an instance of ObjcCppSemantics
-   *
-   * @param enableModules whether modules are enabled
-   */
-  public ObjcCppSemantics(boolean enableModules) {
-    this.enableModules = enableModules;
-  }
+  private ObjcCppSemantics() {}
 
   @Override
   public void finalizeCompileActionBuilder(
@@ -88,10 +78,7 @@ public void validateAttributes(RuleContext ruleContext) {
 
   @Override
   public boolean needsIncludeValidation() {
-    // We disable include validation when modules are enabled, because Apple uses absolute paths in
-    // its module maps, which include validation does not recognize.  Modules should only be used
-    // rarely and in third party code anyways.
-    return !enableModules;
+    return true;
   }
 
   /** cc_shared_library is not supported with Objective-C */

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

@@ -523,7 +523,7 @@ private CompilationResult ccCompileAndLink(
   }
 
   ObjcCppSemantics createObjcCppSemantics() {
-    return attributes.enableModules() ? ObjcCppSemantics.MODULES : ObjcCppSemantics.NO_MODULES;
+    return ObjcCppSemantics.INSTANCE;
   }
 
   private FeatureConfiguration getFeatureConfiguration(