This commit updates the new symbol addressing made for aix/ppc64 according
to feedbacks given in CL 151039.

Change-Id: Ic4eb9943dc520d65f7d084adf8fa9a2530f4d3f9
Reviewed-on: https://go-review.googlesource.com/c/151302
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>