Make building seccomp-bpf a GYP condition

sandbox/linux/sandbox_linux.gypi

 # 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': [
       ['OS=="linux"', {
         'compile_suid_client': 1,
         'compile_credentials': 1,
       }, {
         'compile_suid_client': 0,
         'compile_credentials': 0,
       }],
-      ['((OS=="linux" or OS=="android") and '
-             '(target_arch=="ia32" or target_arch=="x64" or '
-              'target_arch=="arm"))', {
-        'compile_seccomp_bpf': 1,
-      }, {
-        'compile_seccomp_bpf': 0,
-      }],
       ['OS=="linux" and (target_arch=="ia32" or target_arch=="x64")', {
         'compile_seccomp_bpf_demo': 1,
       }, {
         'compile_seccomp_bpf_demo': 0,
       }],
     ],
   },
   'target_defaults': {
     'target_conditions': [
       # All linux/ files will automatically be excluded on Android
       # so make sure we re-include them explicitly.
       ['OS == "android"', {
         'sources/': [
           ['include', '^linux/'],
         ],
       }],
     ],
   },
   'targets': [
     # We have two principal targets: sandbox and sandbox_linux_unittests
     # All other targets are listed as dependencies.
-    # FIXME(jln): for historial reasons, sandbox_linux is the setuid sandbox
-    # and is its own target.
+    # There is one notable exception: for historical reasons, chrome_sandbox is
+    # the setuid sandbox and is its own target.
     {
       'target_name': 'sandbox',
       'type': 'none',
       'dependencies': [
         'sandbox_services',
       ],
       'conditions': [
         [ 'compile_suid_client==1', {
           'dependencies': [
             'suid_sandbox_client',
           ],
         }],
         # Compile seccomp BPF when we support it.
-        [ 'compile_seccomp_bpf==1', {
+        [ 'use_seccomp_bpf==1', {
           'dependencies': [
             'seccomp_bpf',
             'seccomp_bpf_helpers',
           ],
         }],
       ],
     },
     {
       # The main sandboxing test target.
       'target_name': 'sandbox_linux_unittests',
@@ skipping 209 matching lines @@
         },
         'dependencies': [
           'sandbox_linux_jni_unittests',
         ],
         'includes': [ '../../build/apk_test.gypi' ],
         }
       ],
     }],
   ],
 }