[libFuzzer] add UninstrumentedTest.cpp (missing from a previous commit)

llvm-svn: 252658

llvm/lib/Fuzzer/test/UninstrumentedTest.cpp

@@ -0,0 +1,8 @@
+// This test should not be instrumented.
+#include <cstdint>
+#include <cstddef>
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  return 0;
+}
+