They're reserved for use by the compiler, standard library, etc. Bug: None Change-Id: I3b5106473b52847b9de406aaab307909b5378dba Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/183440 Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org> Commit-Queue: Karl Wiberg <kwiberg@webrtc.org> Cr-Commit-Position: refs/heads/master@{#32038}