gn: make some warning flags match gyp more closely

third_party/cython/rules.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 template("python_binary_module") {
   # Only available on linux for now.
   assert(is_linux)
   assert(defined(invoker.sources))
   assert(defined(invoker.python_base_module))
 
@@ skipping 34 matching lines @@
     python_flags = "//third_party/cython/python_flags.py"
     include_dirs = exec_script(python_flags,
                                [ "--gn", "--includes" ],
                                "list lines")
     libs = exec_script(python_flags,
                        [ "--gn", "--libraries" ],
                        "list lines")
     lib_dirs = exec_script(python_flags,
                            [ "--gn", "--library_dirs" ],
                            "list lines")
+    if (!is_win) {
+      # Generated code includes static utility functions that often go unused.
+      cflags = [
+        "-Wno-unused-function",
+      ]
+    }
   }
 
   shared_library(shared_library_name) {
     visibility = target_visibility
     deps = [
       ":$generator_target_name",
     ]
     if (defined(invoker.deps)) {
       deps += invoker.deps
     }
@@ skipping 10 matching lines @@
       "$root_out_dir/${shared_library_prefix}${shared_library_name}${shared_library_suffix}"
     ]
     outputs = [
       "$root_out_dir/python/$python_base_module/${target_name}${python_module_suffix}"
     ]
     deps = [
       ":$shared_library_name"
     ]
   }
 }