Add an option to prune unwanted targets

test/prune_targets/test1.gyp

Index: test/prune_targets/test1.gyp
diff --git a/test/prune_targets/test1.gyp b/test/prune_targets/test1.gyp
new file mode 100644
index 0000000000000000000000000000000000000000..b65ec19fa4c02d28e41447ba91f64e69b087e8fe
--- /dev/null
+++ b/test/prune_targets/test1.gyp
@@ -0,0 +1,26 @@
+# Copyright (c) 2013 Google Inc. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+{
+  'targets': [
+    {
+      'target_name': 'program1',
+      'type': 'executable',
+      'sources': [ 'program.cc' ],
+      'dependencies': [ 'test2.gyp:lib1' ],
+    },
+    {
+      'target_name': 'program2',
+      'type': 'executable',
+      'sources': [ 'program.cc' ],
+      'dependencies': [ 'test2.gyp:lib2' ],
+    },
+    {
+      'target_name': 'program3',
+      'type': 'executable',
+      'sources': [ 'program.cc' ],
+      'dependencies': [ 'test2.gyp:lib3' ],
+    },
+  ],
+}