[libFuzzer] move the implementation of the fork mode into a separate file

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer@353891 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/FuzzerIO.cpp b/FuzzerIO.cpp
index ba4153b..91e1d20 100644
--- a/FuzzerIO.cpp
+++ b/FuzzerIO.cpp
@@ -8,9 +8,10 @@
 // IO functions.
 //===----------------------------------------------------------------------===//
 
-#include "FuzzerIO.h"
 #include "FuzzerDefs.h"
 #include "FuzzerExtFunctions.h"
+#include "FuzzerIO.h"
+#include "FuzzerUtil.h"
 #include <algorithm>
 #include <cstdarg>
 #include <fstream>
@@ -141,4 +142,9 @@
     RemoveFile(F);
 }
 
+std::string TempPath(const char *Extension) {
+  return DirPlusFile(TmpDir(),
+                     "libFuzzerTemp." + std::to_string(GetPid()) + Extension);
+}
+
 }  // namespace fuzzer