Prepare for clang 21

bmcweb doesn't pass these two warnings on clang 21.  We should look into
them at some point as the failures look valid, but ignore them for now
to ungate upgrading the compiler.

Tested:
Build succeeds with clang-21

Change-Id: I67939a9668aa6710cb107bf9b9867835e178ff79
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/meson.build b/meson.build
index 0038115..d24437d 100644
--- a/meson.build
+++ b/meson.build
@@ -102,6 +102,15 @@
         '-Wno-weak-vtables',
         language: 'cpp',
     )
+    if (cxx.version().version_compare('>=21.0'))
+        # TODO(Ed) These warnings look valid and need cleaned up.
+        add_project_arguments(
+            '-Wno-unique-object-duplication',
+            '-Wno-nrvo',
+            language: 'cpp',
+        )
+    endif
+
     boost_flags += ['-Wno-strict-prototypes', '-Wno-unused-but-set-variable']
     nghttp2_flags += ['-Wno-extra-semi']
 endif