cmd/compile: pass struct field note information along in exported info

This is needed to make field tracking work correctly.

Change-Id: I0c3452a48d6f36862f6ee8aacc001813866c0ad4
Reviewed-on: https://go-review.googlesource.com/c/go/+/312069
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/cmd/compile/internal/typecheck/iexport.go

@@ -749,6 +749,7 @@ func (w *exportWriter) exoticParam(f *types.Field) {
 	w.uint64(uint64(f.Offset))
 	w.exoticType(f.Type)
 	w.bool(f.IsDDD())
+	w.string(f.Note)
 }
 func (w *exportWriter) exoticSym(s *types.Sym) {
 	if s == nil {

src/cmd/compile/internal/typecheck/iimport.go

@@ -592,6 +592,7 @@ func (r *importReader) exoticParam() *types.Field {
 		f.Nname = ir.NewNameAt(pos, sym)
 	}
 	f.SetIsDDD(ddd)
+	f.Note = r.string()
 	return f
 }