cmd/compile: use correct packages when exporting/importing _ (blank) names

1) Blank parameters cannot be accessed so the package doesn't matter.
   Do not export it, and consistently use localpkg when importing a
   blank parameter.

2) More accurately replicate fmt.go and parser.go logic when importing
   a blank struct field. Blank struct fields get exported without
   package qualification.
   (This is actually incorrect, even with the old textual export format,
   but we will fix that in a separate change. See also issue 15514.)

Fixes #15491.

Change-Id: I7978e8de163eb9965964942aee27f13bf94a7c3c
Reviewed-on: https://go-review.googlesource.com/22714
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

0 files changed, 0 insertions, 0 deletions