cmd/compile/internal/typecheck: remove iexport assumption of LocalPkg.Path == ""
The indexed export data format encodes the local package's path as "",
because that's historically how we've represented it within
cmd/compile. The format also requires the local package to be first in
the exported list of packages, and was implicitly relying on ""
sorting before other, non-empty package paths.
We can't change the format without breaking existing importers (e.g.,
go/internal/gcimporter), but we can at least remove the dependency on
LocalPkg.Path being "".
Prep refactoring for CL 393715.
Updates #51734.
Change-Id: I6dd4eafd2d538f4e81376948ef9e92fc44a5462a
Reviewed-on: https://go-review.googlesource.com/c/go/+/406057
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com> Reviewed-by: David Chase <drchase@google.com>