Enable native targets used for non-SFI

We currently don't allow native target for clang_nacl, but we need to
lift this restriction to enable the use of nacl-clang to build support
libraries for non-SFI mode.

BUG= None
R=dschuff@chromium.org

Review URL: https://codereview.chromium.org/1283983002 .
1 file changed