cmd/compile: make compilation deterministic, fixes toolstash

Make sure we don't depend on map iterator order.

Fixes #14600

Change-Id: Iac0e0c8689f3ace7a4dc8e2127e2fd3c8545bd29
Reviewed-on: https://go-review.googlesource.com/20158
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/ssa/print.go

@@ -143,7 +143,7 @@ func fprintFunc(p funcPrinter, f *Func) {
 
 		p.endBlock(b)
 	}
-	for name, vals := range f.NamedValues {
-		p.named(name, vals)
+	for _, name := range f.Names {
+		p.named(name, f.NamedValues[name])
 	}
 }