[Piglit] [PATCH] egl_khr_create_context: Fix build error with old eglext.h

[Ken Phillis Jr]

This patch is looking good, and the only change I'd suggest is using
"#ifndef EGL_OPENGL_ES3_BIT_KHR" and "#endif" around the define for
EGL_OPENGL_ES3_BIT_KHR since some compilers might fail due to a
possible redefine.