[Tizen] Disable NaCl on 32-bit builds.

Google has stopped shipping a 32-bit PNaCl toolchain from M39 on, so we
cannot build the NaCl/PNaCl code from fully 32-bit hosts anymore.

See https://code.google.com/p/chromium/issues/detail?id=416235 and
https://groups.google.com/a/chromium.org/forum/#!topic/chromium-packagers/mxPyPeoMwxk
for more information.