runtime: Recognize morestack.S if there is no function name.
runtime: Recognize morestack.S if there is no function name.

R=iant
CC=gofrontend-dev
https://golang.org/cl/7232069

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