rename some _linux files to _posix and introduce os_bsd

The os_bsd variable is only available on FreeBSD and OpenBSD.
Later on others like NetBSD and DragonflyBSD can be added.
This variable was introduced in order to have shorter
conditions in the gyp files.

BUG=
TEST=compile

Patch by Robert Nagy <robert.nagy@gmail.com>
Review URL: http://codereview.chromium.org/8567001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@109929 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed