[build][c++23] Allow deprecations in Vulkan validation layers

There's a use of a std::aligned_union which is deprecated in C++23, but
this is gone in newer upstream versions of the code. But the upstream
code has changed significantly, so patching our version would make
updating harder, and updating to the latest upstream code may be
non-trivial.

Bug: 459923005
Change-Id: Ibc8a98536f195010a89d32fd5dc6534ce8628641
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/Vulkan-ValidationLayers/+/1577879
Commit-Queue: Ian McKellar <ianloic@google.com>
Fuchsia-Auto-Submit: Ian McKellar <ianloic@google.com>
Reviewed-by: Craig Stout <cstout@google.com>

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index f722cb7..933cb22 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -61,6 +61,7 @@
     configs = [
       "//build/config:Wno-unused-but-set-variable",
       "//build/config:Wno-unused-result",
+      "//build/config:Wno-deprecated-declarations",
     ]
   }
   if (is_clang) {