[libFuzzer] print a stack trace on timeout

llvm-svn: 250571
diff --git a/llvm/lib/Fuzzer/FuzzerInternal.h b/llvm/lib/Fuzzer/FuzzerInternal.h
index c672f23..a720adb 100644
--- a/llvm/lib/Fuzzer/FuzzerInternal.h
+++ b/llvm/lib/Fuzzer/FuzzerInternal.h
@@ -56,6 +56,7 @@
 bool IsASCII(const Unit &U);
 
 int NumberOfCpuCores();
+int GetPid();
 
 // Dictionary.