egl/dri2: consistently use ifndef guards over pragma once

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Vedran Miletić <vedran@miletic.net>
Acked-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>

src/egl/drivers/dri2/egl_dri2_fallbacks.h

@@ -22,7 +22,8 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
-#pragma once
+#ifndef EGL_DRI2_FALLBACKS_INCLUDED
+#define EGL_DRI2_FALLBACKS_INCLUDED
 
 #include "egltypedefs.h"
 
@@ -116,3 +117,5 @@ dri2_fallback_get_sync_values(_EGLDisplay *dpy, _EGLSurface *surf,
 {
    return EGL_FALSE;
 }
+
+#endif /* EGL_DRI2_FALLBACKS_INCLUDED */