Add an iexport.go (and corresponding iexport_test.go) file, which is an
adapted version of $GOROOT/src/cmd/compile/internal/gc/iexport.go. This
code writes exportdata for a *go/types.Package.
A majority of this code is directly copied from iexport.go, with a
change of types, while some of it had to be modified slightly.
Updates golang/go#28260
Change-Id: Ic7e8e99f0c6b886839280b410afffb037da8a79b
Reviewed-on: https://go-review.googlesource.com/c/156901
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
58ecf64b2c