use_x11 is better than is_linux for xdisplaycheck dep in mandoline gn build

mandoline/BUILD.gn

Index: mandoline/BUILD.gn
diff --git a/mandoline/BUILD.gn b/mandoline/BUILD.gn
index 41a85258a10d4dc6bcb6672ccba8cee74ea6c6c8..a9b396d12ffe9ee4d15fef6fa2f8c2a022ddd561 100644
--- a/mandoline/BUILD.gn
+++ b/mandoline/BUILD.gn
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/ui.gni")
+
 group("all") {
   # Meta-target, don't link into production code.
   testonly = true
@@ -21,7 +23,7 @@ group("tests") {
     "//mojo:tests",
   ]
 
-  if (is_linux) {
+  if (use_x11) {
     deps += [ "//tools/xdisplaycheck" ]
   }