all: add GLES_SILENCE_DEPRECATION to suppress warnings

Change-Id: I8544e7cd8c4e3d2b71fd1850f7043eabe25231d0
Reviewed-on: https://go-review.googlesource.com/c/mobile/+/374497
Run-TryBot: Hajime Hoshi <hajimehoshi@gmail.com>
Trust: Hajime Hoshi <hajimehoshi@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

Author: hajimehoshi

app/darwin_ios.m

@@ -10,6 +10,8 @@
 #include <stdio.h>
 #include <sys/utsname.h>
 
+#define GLES_SILENCE_DEPRECATION
+
 #import <UIKit/UIKit.h>
 #import <GLKit/GLKit.h>
 

gl/work.h

@@ -15,6 +15,7 @@
 #endif
 
 #ifdef os_ios
+#define GLES_SILENCE_DEPRECATION
 #include <OpenGLES/ES2/glext.h>
 #endif