cmd/gc: compute initialization order for top-level blank vars too.

Fixes #5244.

R=golang-dev, rsc, iant, r, daniel.morsing
CC=golang-dev
https://golang.org/cl/8601044

src/cmd/gc/sinit.c

@@ -53,9 +53,7 @@ init1(Node *n, NodeList **out)
 		if(isblank(n) && n->curfn == N && n->defn != N && n->defn->initorder == InitNotStarted) {
 			// blank names initialization is part of init() but not
 			// when they are inside a function.
-			n->defn->initorder = InitDone;
-			if(debug['%']) dump("nonstatic", n->defn);
-			*out = list(*out, n->defn);
+			break;
 		}
 		return;
 	}
@@ -130,7 +128,7 @@ init1(Node *n, NodeList **out)
 				init2(n->defn->right, out);
 				if(debug['j'])
 					print("%S\n", n->sym);
-				if(!staticinit(n, out)) {
+				if(isblank(n) || !staticinit(n, out)) {
 					if(debug['%']) dump("nonstatic", n->defn);
 					*out = list(*out, n->defn);
 				}

test/fixedbugs/issue5244.go

+// run
+
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 5244: the init order computation uses the wrong
+// order for top-level blank identifier assignments.
+// The example used to panic because it tries calling a
+// nil function instead of assigning to f before.
+
+package main
+
+var f = func() int { return 1 }
+var _ = f() + g()
+var g = func() int { return 2 }
+
+func main() {}