Add 'third_party/subzero/' from commit 'fb705a6d'
from repository https://chromium.googlesource.com/native_client/pnacl-subzero

Bug swiftshader:47
Bug b/37478805

Change-Id: I9cc7a7f3d788059984102c8275ec7b28c4b0aad0
git-subtree-dir: third_party/subzero
git-subtree-mainline: 1ba2611b
git-subtree-split: fb705a6d