gc: Preserve original blank name for .anon substitution on out params.

Fixes #1802.

R=rsc
CC=golang-dev
https://golang.org/cl/5364043
diff --git a/test/fixedbugs/bug377.dir/one.go b/test/fixedbugs/bug377.dir/one.go
new file mode 100644
index 0000000..c906075
--- /dev/null
+++ b/test/fixedbugs/bug377.dir/one.go
@@ -0,0 +1,6 @@
+package one
+
+func Foo() (n int64, _ *int) {
+	return 42, nil
+}
+
diff --git a/test/fixedbugs/bug377.dir/two.go b/test/fixedbugs/bug377.dir/two.go
new file mode 100644
index 0000000..8a5346a
--- /dev/null
+++ b/test/fixedbugs/bug377.dir/two.go
@@ -0,0 +1,4 @@
+package two
+
+import _ "./one"
+
diff --git a/test/fixedbugs/bug377.go b/test/fixedbugs/bug377.go
new file mode 100644
index 0000000..b6b5509
--- /dev/null
+++ b/test/fixedbugs/bug377.go
@@ -0,0 +1,9 @@
+// $G $D/$F.dir/one.go && $G $D/$F.dir/two.go
+
+// Copyright 2011 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 1802
+
+ignored