cmd/compile/internal/gc: shrink Sym by 8 bytes on amd64

Move 8-bit flags field after 32-bit Block field

Change-Id: I8e5e9a2285477aac2402a839a105e710d5340224
Reviewed-on: https://go-review.googlesource.com/37848
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -51,15 +51,14 @@ type Sym struct {
 	Pkg        *Pkg
 	Name       string   // object name
 	Def        *Node    // definition: ONAME OTYPE OPACK or OLITERAL
-	Block      int32    // blocknumber to catch redeclaration
 	Lastlineno src.XPos // last declaration for diagnostic
+	Block      int32    // blocknumber to catch redeclaration
 
+	flags   bitset8
 	Label   *Node // corresponding label (ephemeral)
 	Origpkg *Pkg  // original package for . import
 	Lsym    *obj.LSym
 	Fsym    *Sym // funcsym
-
-	flags bitset8
 }
 
 const (

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

@@ -26,7 +26,7 @@ func TestSizeof(t *testing.T) {
 		{Name{}, 36, 56},
 		{Param{}, 28, 56},
 		{Node{}, 84, 136},
-		{Sym{}, 64, 120},
+		{Sym{}, 64, 112},
 		{Type{}, 60, 96},
 		{MapType{}, 20, 40},
 		{ForwardType{}, 20, 32},