Fix build.sh sdk function
Fix build.sh sdk function

The core sdk build in build.sh is no longer used by the translator
build, but it is still called externally by the FYI toolchain
bots and by the spec script. rev 1fceb450c8ec changed build.sh
to use toolchain_build's translator_compiler location to
build the sandboxed translator, but it also affected the
sdk function.
This CL fixes the SDK function to be more freestanding.

BUG=red bots
R=jfb@chromium.org, jvoung@chromium.org

Review URL: https://codereview.chromium.org/849153003

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client