Make udev target disappear on linux when use_udev==0

build/linux/system.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'conditions': [
       ['sysroot!=""', {
         'pkg-config': '<(chroot_cmd) ./pkg-config-wrapper "<(sysroot)" "<(target_arch)" "<(system_libdir)"',
       }, {
@@ skipping 420 matching lines @@
             ],
           },
           'link_settings': {
             'libraries': [
               '<!@(<(pkg-config) --libs-only-l libdrm)',
             ],
           },
         },
       ],
     }],
+    ['use_udev==1', {
+      'targets': [
+        {
+          'target_name': 'udev',
+          'type': 'none',
+          'conditions': [
+            ['_toolset=="target"', {
+              'direct_dependent_settings': {
+                'cflags': [
+                  '<!@(<(pkg-config) --cflags libudev)'
+                ],
+              },
+              'link_settings': {
+                'ldflags': [
+                  '<!@(<(pkg-config) --libs-only-L --libs-only-other libudev)',
+                ],
+                'libraries': [
+                  '<!@(<(pkg-config) --libs-only-l libudev)',
+                ],
+              },
+            }],
+          ],
+        },
+      ],
+    }],
   ],  # conditions
   'targets': [
     {
       'target_name': 'dbus',
       'type': 'none',
       'direct_dependent_settings': {
         'cflags': [
           '<!@(<(pkg-config) --cflags dbus-1)',
         ],
       },
@@ skipping 574 matching lines @@
                   # There is a broken header guard in /usr/include/nss/secmod.h:
                   # https://bugzilla.mozilla.org/show_bug.cgi?id=884072
                   '-Wno-header-guard',
                 ],
               },
             }],
           ]
         }],
       ],
     },
-    {
-      'target_name': 'udev',
-      'type': 'none',
-      'conditions': [
-        # libudev is not available on *BSD
-        ['_toolset=="target" and os_bsd!=1', {
-          'direct_dependent_settings': {
-            'cflags': [
-              '<!@(<(pkg-config) --cflags libudev)'
-            ],
-          },
-          'link_settings': {
-            'ldflags': [
-              '<!@(<(pkg-config) --libs-only-L --libs-only-other libudev)',
-            ],
-            'libraries': [
-              '<!@(<(pkg-config) --libs-only-l libudev)',
-            ],
-          },
-        }],
-      ],
-    },
   ],
 }