Only use protected visibility on ELF targets.
Only use protected visibility on ELF targets.

R=iant
https://golang.org/cl/223056

qskycolor/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,golang/gofrontend,anlhord/gofrontend,anlhord/gofrontend,anlhord/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,golang/gofrontend,golang/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend