[llvm-objdump/mac] Silence XAR deprecation warning (NFC)

[keith]

Summary

If you're building this on macOS 12.x+ this produces a deprecation
warning. I'm not sure what this means for the bitcode format going
forward, but it seems safe to silence for now.

[int3]

seems reasonable

llvm/tools/llvm-objdump/MachODump.cpp

 typedef std::pair<uint64_t, DiceRef> DiceTableEntry;
 typedef std::vector<DiceTableEntry> DiceTable;
 typedef DiceTable::iterator dice_table_iterator;
 
 #ifdef LLVM_HAVE_LIBXAR
 namespace {
 struct ScopedXarFile {
   xar_t xar;
-  ScopedXarFile(const char *filename, int32_t flags)
-      : xar(xar_open(filename, flags)) {}
+  ScopedXarFile(const char *filename, int32_t flags) {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+    xar = xar_open(filename, flags);
+#pragma clang diagnostic pop
+  }
   ~ScopedXarFile() {
     if (xar)
       xar_close(xar);
   }
   ScopedXarFile(const ScopedXarFile &) = delete;
   ScopedXarFile &operator=(const ScopedXarFile &) = delete;
   operator xar_t() { return xar; }
 };