cgo: don't overwrite p.Crefs
cgo: don't overwrite p.Crefs

It's expected to be shared between all files so that all types are output.
Fixes bug reported on mailing list by Peter Froehlich.

R=rsc, phf
CC=golang-dev
http://codereview.appspot.com/183043

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go