Otherwise Clang has to assign a file entry to the label which conflicts with
later, explicit, file entries.

Change-Id: Ifc782821517aa7b48ba3ef304d4468f2bc850ac2
Reviewed-on: https://boringssl-review.googlesource.com/27544
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>