The headers are within the same framework called OpenGLES. They are found in
OpenGLES.framework/Headers/ES1 and OpenGLES.framework/Headers/ES2.
so from the earlier compilation error would theoretically be fixed with
#import <OpenGLES/ES1/gl.h>
#import <OpenGLES/ES1/glext.h>
or
#import <OpenGLES/ES2/gl.h>
#import <OpenGLES/ES2/glext.h>
gles2gsg.h:44:23: error: GLES2/gl2.h: No such file or directory
gles2gsg.h:45:26: error: GLES2/gl2ext.h: No such file or directory