cmd/compile: change Func.{Enter,Exit} from NodeList to slice

Introduces a new types Nodes that can be used to replace NodeList.

Update #14473.

Change-Id: Id77c5dcae0cbeb898ba12dd46bd400aad408871c
Reviewed-on: https://go-review.googlesource.com/19969
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/cmd/compile/internal/gc/gen.go b/src/cmd/compile/internal/gc/gen.go
index adebfb8..4edef2b 100644
--- a/src/cmd/compile/internal/gc/gen.go
+++ b/src/cmd/compile/internal/gc/gen.go
@@ -219,6 +219,12 @@
 	}
 }
 
+func Genslice(l []*Node) {
+	for _, n := range l {
+		gen(n)
+	}
+}
+
 // generate code to start new proc running call n.
 func cgen_proc(n *Node, proc int) {
 	switch n.Left.Op {