go/loader: don't create types.Package for "unsafe"

https://golang.org/cl/37694 is a backwards-incompatible change to the
go/types API that causes "unsafe" to be included among the results of
(*types.Package).Imports().  Client packages such as go/loader and
go/ssa now need to recognize the special unsafe package and its
unusual *Bultin members and not create a types.Package for it.

Change-Id: I902725d3053cb887246978efdb5ec5dcdc0e4818
Reviewed-on: https://go-review.googlesource.com/37710
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
2 files changed