cmd/cgo: use debug data for enums on windows
cmd/cgo: use debug data for enums on windows

Use the debug data for enums on windows.

Fixes issue 4120.

R=alex.brainman
CC=golang-dev
http://codereview.appspot.com/6545047
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go