Fix Wgnu-folding-constant.

This CL fixes "variable length array folded to constant array as an
extension" by switching the constant variable declaration to an enum,
which is compile-time constant.

Bug: None
Change-Id: Iff8cd22e6320a19439fc3f1ae2fb7126210e080b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227642
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34651}

examples/objc/AppRTCMobile/third_party/SocketRocket/SRWebSocket.m

@@ -1478,7 +1478,7 @@ static const size_t SRFrameHeaderOverhead = 32;
                 
             case NSStreamEventHasBytesAvailable: {
                 SRFastLog(@"NSStreamEventHasBytesAvailable %@", aStream);
-                const int bufferSize = 2048;
+                enum EnumType : int { bufferSize = 2048 };
                 uint8_t buffer[bufferSize];
 
                 while (self->_inputStream.hasBytesAvailable) {