add the fuzzer from oss-fuzz and a test that exercises it

test/fuzz_unpack_pack_fuzzer.cpp

@@ -0,0 +1,10 @@
+#include <gtest/gtest.h>
+
+#include "../fuzz/unpack_pack_fuzzer.cc"
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size);
+
+TEST(FUZZ_UNPACK_PACK_FUZZER, works)
+{
+  EXPECT_EQ(0, LLVMFuzzerTestOneInput(0, 0));
+}