DWARF doesn't work for buildmode exe binaries; see golang.org/issues/25148. Fixes golang/go#25148. Change-Id: I511599f3d1963ff0b3e48ac5c8cce50ee6aa54de Reviewed-on: https://go-review.googlesource.com/110059 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>