fix compile error when EGL_BUFFER_AGE_EXT is missing

Signed-off-by: Adrian Negreanu <adrian.m.negreanu@intel.com>

clients/simple-egl.c

@@ -38,6 +38,8 @@
 #include <EGL/egl.h>
 #include <EGL/eglext.h>
 
+#include <src/weston-egl-ext.h>
+
 #ifndef EGL_EXT_swap_buffers_with_damage
 #define EGL_EXT_swap_buffers_with_damage 1
 typedef EGLBoolean (EGLAPIENTRYP PFNEGLSWAPBUFFERSWITHDAMAGEEXTPROC)(EGLDisplay dpy, EGLSurface surface, EGLint *rects, EGLint n_rects);