[clang-objc-fuzzer] Add LLVMFuzzerInitialize to fix msvc builds (PR44414)

The (supposedly superfluous) LLVMFuzzerInitialize function was removed when this file was copied from clang-fuzzer, but this is causing link errors on some targets. @morehouse confirmed on D69171 that it was OK to add back.

clang/tools/clang-fuzzer/ClangObjectiveCFuzzer.cpp

@@ -16,6 +16,8 @@
 
 using namespace clang_fuzzer;
 
+extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) { return 0; }
+
 extern "C" int LLVMFuzzerTestOneInput(uint8_t *data, size_t size) {
   std::string s(reinterpret_cast<const char *>(data), size);
   HandleCXX(s, "./test.m", {"-O2"});