Compile rtc_api_objc on Mac.

webrtc/api/objc/RTCIceServer.mm

Index: webrtc/api/objc/RTCIceServer.mm
diff --git a/webrtc/api/objc/RTCIceServer.mm b/webrtc/api/objc/RTCIceServer.mm
index 057c69603b0cfb1f5e9c559bb9467c8bec1c7fe2..8cb3c513d786ceec3338b51a6db436afef15f5d4 100644
--- a/webrtc/api/objc/RTCIceServer.mm
+++ b/webrtc/api/objc/RTCIceServer.mm
@@ -19,14 +19,14 @@
 @synthesize username = _username;
 @synthesize credential = _credential;
 
-- (instancetype)initWithURLStrings:(NSArray<NSString *> *)urlStrings {
+- (instancetype)initWithURLStrings:(NSArray/*<NSString *>*/ *)urlStrings {
   NSParameterAssert(urlStrings.count);
   return [self initWithURLStrings:urlStrings
                          username:nil
                        credential:nil];
 }
 
-- (instancetype)initWithURLStrings:(NSArray<NSString *> *)urlStrings
+- (instancetype)initWithURLStrings:(NSArray/*<NSString *>*/ *)urlStrings
                           username:(NSString *)username
                         credential:(NSString *)credential {
   NSParameterAssert(urlStrings.count);