Support more configurability in GN toolchains

tools/gn/example/hello.cc

Index: tools/gn/example/hello.cc
diff --git a/tools/gn/example/hello.cc b/tools/gn/example/hello.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c4aa4482949cd0ea980a563e2ea9c5cd2e118365
--- /dev/null
+++ b/tools/gn/example/hello.cc
@@ -0,0 +1,13 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stdio.h>
+
+#include "hello_shared.h"
+#include "hello_static.h"
+
+int main(int argc, char* argv[]) {
+  printf("%s, %s\n", GetStaticText(), GetSharedText());
+  return 0;
+}