Update attributes to match gclibc's ansidecl.h

To ease use of WebRTC in other codebases, update some macros
to match glibc's ansidecl.h, which uses double-underscores for attributes.

NOTRY=True

Review URL: https://codereview.webrtc.org/1571653002

Cr-Original-Commit-Position: refs/heads/master@{#11185}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: b71b4f0c7af57ef5b676c6ed70bf945282c90e3a
4 files changed