[lld-macho] Silence XAR deprecation warning

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.

Do we need to worry about GCC for this?

Differential Revision: https://reviews.llvm.org/D117718

lld/MachO/SyntheticSections.cpp

@@ -1283,7 +1283,10 @@ void BitcodeBundleSection::finalize() {
   using namespace llvm::sys::fs;
   CHECK_EC(createTemporaryFile("bitcode-bundle", "xar", xarPath));
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
   xar_t xar(xar_open(xarPath.data(), O_RDWR));
+#pragma clang diagnostic pop
   if (!xar)
     fatal("failed to open XAR temporary file at " + xarPath);
   CHECK_EC(xar_opt_set(xar, XAR_OPT_COMPRESSION, XAR_OPT_VAL_NONE));