Update subzero bitcode parser to use new API for bitstream reading.

Dependent on https://codereview.chromium.org/1122423005
being committed first.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=4164
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/1130313002
1 file changed