[cpp] Suppress warning for C++20

 We need -Wno-ambiguous-reversed-operator to build in C++20 mode.

 Test: Add --experimenatl_cxx_version=20 to args.gn and fx build

Change-Id: I3de3e3bd703d264c4a2b6bf48744c5f9d5c3a387
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/Vulkan-Tools/+/635802
Reviewed-by: David Reveman <reveman@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 14b8e27..67d3273 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -98,6 +98,7 @@
       "-Wno-implicit-fallthrough",
       "-Wno-missing-field-initializers",
       "-Wno-extra-semi",
+      "-Wno-ambiguous-reversed-operator",
     ]
   }