cmd/internal/gc: convert yet more Node fields to bools

Convert Embedded, Method, and Colas to bools.

I believe that this is the last of the Node fields
that can be trivially converted to bools.

No functional changes. Passes toolstash -cmp.

Change-Id: I81962ee47866596341fc60d24d6959c20cd7fc1c
Reviewed-on: https://go-review.googlesource.com/8440
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/8g/cgen64.go b/src/cmd/8g/cgen64.go
index ee04bdb..7fb6549 100644
--- a/src/cmd/8g/cgen64.go
+++ b/src/cmd/8g/cgen64.go
@@ -63,14 +63,14 @@
 
 	l := n.Left
 	r := n.Right
-	if l.Addable == 0 {
+	if !l.Addable {
 		var t1 gc.Node
 		gc.Tempname(&t1, l.Type)
 		gc.Cgen(l, &t1)
 		l = &t1
 	}
 
-	if r != nil && r.Addable == 0 {
+	if r != nil && !r.Addable {
 		var t2 gc.Node
 		gc.Tempname(&t2, r.Type)
 		gc.Cgen(r, &t2)