Remove the built in flag from ObjC interfaces (#487)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1a577da..6f64cf7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,14 @@
+# 7.2.1
+
+- Fix helper methods sometimes missing from NSString.
+
 # 7.2.0
+
 - Added support for sharing bindings using `symbol-file` config. (See `README.md`
 and examples/shared_bindings).
 
 # 7.1.0
+
 - Handle declarations with definition accessible from a different entry-point.
 
 # 7.0.0
diff --git a/lib/src/code_generator/objc_built_in_functions.dart b/lib/src/code_generator/objc_built_in_functions.dart
index d796763..e7f5bd5 100644
--- a/lib/src/code_generator/objc_built_in_functions.dart
+++ b/lib/src/code_generator/objc_built_in_functions.dart
@@ -311,7 +311,6 @@
         (ObjCInterface(
           originalName: "NSData",
           builtInFunctions: this,
-          isBuiltIn: true,
         ));
   }
 
diff --git a/lib/src/code_generator/objc_interface.dart b/lib/src/code_generator/objc_interface.dart
index cda85ca..8ca0b8e 100644
--- a/lib/src/code_generator/objc_interface.dart
+++ b/lib/src/code_generator/objc_interface.dart
@@ -44,7 +44,6 @@
 
   final String lookupName;
   final ObjCBuiltInFunctions builtInFunctions;
-  final bool isBuiltIn;
   late final ObjCInternalGlobal _classObject;
   late final ObjCInternalGlobal _isKindOfClass;
   late final Func _isKindOfClassMsgSend;
@@ -56,7 +55,6 @@
     String? lookupName,
     String? dartDoc,
     required this.builtInFunctions,
-    required this.isBuiltIn,
   })  : lookupName = lookupName ?? originalName,
         super(
           usr: usr,
@@ -64,13 +62,11 @@
           name: name ?? originalName,
           dartDoc: dartDoc,
         ) {
-    if (isBuiltIn) {
-      builtInFunctions.registerInterface(this);
-    }
+    builtInFunctions.registerInterface(this);
   }
 
-  bool get isNSString => isBuiltIn && originalName == "NSString";
-  bool get isNSData => isBuiltIn && originalName == "NSData";
+  bool get isNSString => originalName == "NSString";
+  bool get isNSData => originalName == "NSData";
 
   @override
   BindingString toBindingString(Writer w) {
diff --git a/lib/src/header_parser/sub_parsers/objcinterfacedecl_parser.dart b/lib/src/header_parser/sub_parsers/objcinterfacedecl_parser.dart
index 16cec51..64f1e28 100644
--- a/lib/src/header_parser/sub_parsers/objcinterfacedecl_parser.dart
+++ b/lib/src/header_parser/sub_parsers/objcinterfacedecl_parser.dart
@@ -75,7 +75,6 @@
     lookupName: config.objcModulePrefixer.applyPrefix(name),
     dartDoc: getCursorDocComment(cursor),
     builtInFunctions: objCBuiltInFunctions,
-    isBuiltIn: cursor.isInSystemHeader(),
   );
 }
 
diff --git a/pubspec.yaml b/pubspec.yaml
index 1608ea8..c5d8d67 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -3,7 +3,7 @@
 # BSD-style license that can be found in the LICENSE file.
 
 name: ffigen
-version: 7.2.0
+version: 7.2.1
 description: Generator for FFI bindings, using LibClang to parse C header files.
 repository: https://github.com/dart-lang/ffigen