Currently go list -test runtime/cgo fails with an index out of range
error. This appears to be because the updating of import paths that
happens as part of -test doesn't take into account the fact that the
Internal.Imports of a package do not contain "C", whereas the public
Imports do.

Therefore we skip the public Import of "C" if it exists and continue.

Change-Id: I5cdc8968890fa7e5da3e375718606037d3282754
Reviewed-on: https://go-review.googlesource.com/111175
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>