Fix defer/recover at high optimization levels.
Fix defer/recover at high optimization levels.

R=iant
CC=gofrontend-dev
https://golang.org/cl/5005049

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