cgo: define idents referenced only from macros

cgo/testdata/const.go

@@ -3,10 +3,13 @@ package main
 /*
 #define foo 3
 #define bar foo
+#define unreferenced 4
+#define referenced unreferenced
 */
 import "C"
 
 const (
 	Foo = C.foo
 	Bar = C.bar
+	Baz = C.referenced
 )

cgo/testdata/const.out.go

@@ -47,3 +47,5 @@ type (
 
 const C.foo = 3
 const C.bar = C.foo
+const C.unreferenced = 4
+const C.referenced = C.unreferenced