cmd/internal/gc, cmd/[56789]g: rename stackcopy to blockcopy

To avoid confusion with the runtime concept of copying stack.

Change-Id: I33442377b71012c2482c2d0ddd561492c71e70d0
Reviewed-on: https://go-review.googlesource.com/8639
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/src/cmd/internal/gc/cgen.go b/src/cmd/internal/gc/cgen.go
index d24db5f..3fea97e 100644
--- a/src/cmd/internal/gc/cgen.go
+++ b/src/cmd/internal/gc/cgen.go
@@ -2312,7 +2312,7 @@
 		return
 	}
 
-	Thearch.Stackcopy(n, ns, osrc, odst, w)
+	Thearch.Blockcopy(n, ns, osrc, odst, w)
 }
 
 /*