runtime: Correct test for morestack.S.
runtime: Correct test for morestack.S.

R=iant
CC=gofrontend-dev
https://golang.org/cl/7230061

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