cmd/compile: move LSym.RefIdx for better packing

Change-Id: I0516d49ee8381c5e022d77c2fb41515c01c8a631
Reviewed-on: https://go-review.googlesource.com/20764
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/internal/obj/link.go

@@ -314,7 +314,6 @@ type LSym struct {
 	Leaf      uint8
 	Seenglobl uint8
 	Onlist    uint8
-	RefIdx    int // Index of this symbol in the symbol reference list.
 
 	// ReflectMethod means the function may call reflect.Type.Method or
 	// reflect.Type.MethodByName. Matching is imprecise (as reflect.Type
@@ -330,7 +329,9 @@ type LSym struct {
 	// visible outside of the module (shared library or executable) that contains its
 	// definition. (When not compiling to support Go shared libraries, all symbols are
 	// local in this sense unless there is a cgo_export_* directive).
-	Local  bool
+	Local bool
+
+	RefIdx int // Index of this symbol in the symbol reference list.
 	Args   int32
 	Locals int32
 	Size   int64

src/cmd/internal/obj/sizeof_test.go

@@ -23,7 +23,7 @@ func TestSizeof(t *testing.T) {
 		_64bit uintptr     // size on 64bit platforms
 	}{
 		{Addr{}, 52, 80},
-		{LSym{}, 84, 144},
+		{LSym{}, 80, 136},
 		{Prog{}, 196, 288},
 	}