cmd/7g: add ARM64 Go compiler, based on 9g

No peep optimizer yet.

Change-Id: Ifa5f993cd6ac5e34783c0df41faf772fbce96ae2
Reviewed-on: https://go-review.googlesource.com/7049
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/src/cmd/internal/gc/walk.go b/src/cmd/internal/gc/walk.go
index e4abc28..4aecd54 100644
--- a/src/cmd/internal/gc/walk.go
+++ b/src/cmd/internal/gc/walk.go
@@ -3625,7 +3625,7 @@
 }
 
 func walkrotate(np **Node) {
-	if Thearch.Thechar == '9' {
+	if Thearch.Thechar == '7' || Thearch.Thechar == '9' {
 		return
 	}
 
@@ -3757,7 +3757,7 @@
 	// if >= 0, nr is 1<<pow // 1 if nr is negative.
 
 	// TODO(minux)
-	if Thearch.Thechar == '9' {
+	if Thearch.Thechar == '7' || Thearch.Thechar == '9' {
 		return
 	}