Fix building recover thunks which return multiple values.
Fix building recover thunks which return multiple values.

R=iant
CC=gofrontend-dev
https://golang.org/cl/3788045

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