Merge pull request #17482 from yleduc/fix_ios_build_es2

fix iOS build - error due to GLES2 missing include

platform/iphone/platform_config.h

@@ -30,6 +30,7 @@
 
 #include <alloca.h>
 
+#define GLES2_INCLUDE_H <ES2/gl.h>
 #define GLES3_INCLUDE_H <ES3/gl.h>
 
 #define PLATFORM_REFCOUNT