Add an option to prune unwanted targets

test/prune_targets/lib_indirect.cc

Index: test/prune_targets/lib_indirect.cc
diff --git a/test/win/shard/hello4.cc b/test/prune_targets/lib_indirect.cc
similarity index 86%
copy from test/win/shard/hello4.cc
copy to test/prune_targets/lib_indirect.cc
index a94df194999a38e80cde7e2a7205a9f6a39601cd..92d9ea40db811b235b37f10542b635a3222d9886 100644
--- a/test/win/shard/hello4.cc
+++ b/test/prune_targets/lib_indirect.cc
@@ -2,6 +2,5 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-int f4() {
-  return 0;
+void libfunc_indirect() {
 }