Add iOS static library GN build script. NOTRY=True

webrtc/modules/audio_device/ios/objc/RTCAudioSessionConfiguration.h

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #import <AVFoundation/AVFoundation.h>
 #import <Foundation/Foundation.h>
 
+#import "WebRTC/RTCMacros.h"
+
 NS_ASSUME_NONNULL_BEGIN
 
 extern const int kRTCAudioSessionPreferredNumberOfChannels;
 extern const double kRTCAudioSessionHighPerformanceSampleRate;
 extern const double kRTCAudioSessionLowComplexitySampleRate;
 extern const double kRTCAudioSessionHighPerformanceIOBufferDuration;
 extern const double kRTCAudioSessionLowComplexityIOBufferDuration;
 
 // Struct to hold configuration values.
+RTC_EXPORT
 @interface RTCAudioSessionConfiguration : NSObject
 
 @property(nonatomic, strong) NSString *category;
 @property(nonatomic, assign) AVAudioSessionCategoryOptions categoryOptions;
 @property(nonatomic, strong) NSString *mode;
 @property(nonatomic, assign) double sampleRate;
 @property(nonatomic, assign) NSTimeInterval ioBufferDuration;
 @property(nonatomic, assign) NSInteger inputNumberOfChannels;
 @property(nonatomic, assign) NSInteger outputNumberOfChannels;
 
 /** Initializes configuration to defaults. */
 - (instancetype)init NS_DESIGNATED_INITIALIZER;
 
 /** Returns the current configuration of the audio session. */
 + (instancetype)currentConfiguration;
 /** Returns the configuration that WebRTC needs. */
 + (instancetype)webRTCConfiguration;
 /** Provide a way to override the default configuration. */
 + (void)setWebRTCConfiguration:(RTCAudioSessionConfiguration *)configuration;
 
 @end
 
 NS_ASSUME_NONNULL_END