ogle/gosym: sync with tip debug/gosym in the standard library.

In particular, pick up
changeset:   19158:737767dd81fd
user:        Russ Cox <rsc@golang.org>
date:        Tue Feb 18 23:41:15 2014 -0500
summary:     cmd/ld: remove Plan 9 symbol table
(code review 65740045)

LGTM=r
R=r
https://golang.org/cl/66720043