.bss section has no data stored in PE file. But when .bss section data
is used by the linker it is assumed that its every byte is set to zero.
(*Section).Data returns garbage at this moment. Change (*Section).Data
so it returns slice filled with 0s.

Updates #15345

Change-Id: I1fa5138244a9447e1d59dec24178b1dd0fd4c5d7
Reviewed-on: https://go-review.googlesource.com/22544Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>