cmd/compile: unexport types.Sym.LSym

Response to code review feedback on CL 40693.

Remove the final reference to it from package gc,
and manually unexport.

Passes toolstash-check.

Change-Id: I7fc48edd43263d8f7c56b47aeb7573408463dc22
Reviewed-on: https://go-review.googlesource.com/41303
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -1338,7 +1338,8 @@ ok:
 			keep = true
 		}
 	}
-	s.Lsym.Set(obj.AttrMakeTypelink, keep)
+	// TODO(josharian): add lsym local variable above, use here instead of calling Linksym()
+	s.Linksym().Set(obj.AttrMakeTypelink, keep)
 
 	return s
 }

src/cmd/compile/internal/types/sym.go

@@ -31,7 +31,7 @@ type Sym struct {
 	flags   bitset8
 	Label   *Node // corresponding label (ephemeral)
 	Origpkg *Pkg  // original package for . import
-	Lsym    *obj.LSym
+	lsym    *obj.LSym
 }
 
 const (
@@ -78,8 +78,8 @@ func (sym *Sym) Linksym() *obj.LSym {
 	if sym == nil {
 		return nil
 	}
-	if sym.Lsym == nil {
-		sym.Lsym = Ctxt.Lookup(sym.LinksymName())
+	if sym.lsym == nil {
+		sym.lsym = Ctxt.Lookup(sym.LinksymName())
 	}
-	return sym.Lsym
+	return sym.lsym
 }