[libFuzzer] move some code from public interface header to a non-public header. NFC

llvm-svn: 257963
diff --git a/llvm/lib/Fuzzer/FuzzerLoop.cpp b/llvm/lib/Fuzzer/FuzzerLoop.cpp
index 9b64e36..4172036 100644
--- a/llvm/lib/Fuzzer/FuzzerLoop.cpp
+++ b/llvm/lib/Fuzzer/FuzzerLoop.cpp
@@ -478,7 +478,7 @@
 void Fuzzer::Loop() {
   system_clock::time_point LastCorpusReload = system_clock::now();
   if (Options.DoCrossOver)
-    USF.SetCorpus(&Corpus);
+    USF.GetMD().SetCorpus(&Corpus);
   while (true) {
     SyncCorpus();
     auto Now = system_clock::now();