This works around a compiler bug that leads to incorrect masking of
the semantic_ field in TruncatingUseInfoFromRepresentation.

Patch from bulach@google.com

BUG=

Review-Url: https://codereview.chromium.org/2669113003
Cr-Original-Commit-Position: refs/heads/master@{#42925}
Committed: https://chromium.googlesource.com/v8/v8/+/8c7fc377fd5c03e30cbf767cd22aba59178e0143
Review-Url: https://codereview.chromium.org/2669113003
Cr-Commit-Position: refs/heads/master@{#43099}