[libFuzzer] add -features_dir= flag to dump unique input features on disk

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer@358317 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/FuzzerIOPosix.cpp b/FuzzerIOPosix.cpp
index 953848a..cfd69bb 100644
--- a/FuzzerIOPosix.cpp
+++ b/FuzzerIOPosix.cpp
@@ -120,6 +120,10 @@
   unlink(Path.c_str());
 }
 
+void RenameFile(const std::string &OldPath, const std::string &NewPath) {
+  rename(OldPath.c_str(), NewPath.c_str());
+}
+
 void DiscardOutput(int Fd) {
   FILE* Temp = fopen("/dev/null", "w");
   if (!Temp)