s.Func.Text only can be nil at the moment, otherwise there has
some bugs in compiler's Go rumtime.

Change-Id: Ib2ff9bb977352838e67f2b98a69468f6f350c1f3
Reviewed-on: https://go-review.googlesource.com/123535Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>