seccomp: simplify enable/disable logic

1) Only compile in seccomp code at all if it's on a platform we
intend to support (non-ChromeOS non-ARM non-Views Linux).
2) Move usage of seccomp code behind a define and usage of seccomp
flags into a function call.

The former helps catch bugs in the latter: it will be a link error
if I accidentally break the enable/disable logic in code.

Review URL: http://codereview.chromium.org/7519016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@94784 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed