window.c: Fix compile/run using cairo without egl
diff --git a/configure.ac b/configure.ac
index badecfe..756b125 100644
--- a/configure.ac
+++ b/configure.ac
@@ -101,7 +101,8 @@
   PKG_CHECK_MODULES(CAIRO_EGL, [cairo-egl >= 1.11.3],
 		    [have_cairo_egl=yes], [have_cairo_egl=no])
   AS_IF([test "x$have_cairo_egl" = "xyes"],
-        [AC_DEFINE([HAVE_CAIRO_EGL], [1], [Have cairo-egl])])
+        [AC_DEFINE([HAVE_CAIRO_EGL], [1], [Have cairo-egl])],
+        [AC_MSG_WARN([Cairo-EGL not found - clients will use cairo image])])
 fi
 
 AM_CONDITIONAL(HAVE_POPPLER, test "x$have_poppler" = "xyes")