[NaCl] Remove legacy nacl_mounts usage.

Also add nacl SDK version check to ensure the SDK contains
a recent version of nacl_io.
[NaCl] Recreate webstore zip archive each build.
[NaCl] Remove use of -lnosys
[NaCl] Don't cache font size

This avoids churn of the cached font when different
sizes of the same font are requested sequentially.

Review URL: https://codereview.chromium.org/14308007
[NaCl] Build for all nacl architectures
[NaCl] Add support for building using glibc toolchain.

BUG=
R=binji@chromium.org

Review URL: https://codereview.chromium.org/14694016
[NaCl] update build-nacl.sh
[NaCl] Remove missing functions from lua stdlib.

NaCl doesn't support tmpfile() or exec() so remove
these from the lua stdlib build when building for NaCl.