Update BUILD.gn with recently added file (#5004)

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 8ad1b4a..a375e9d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -539,6 +539,7 @@
     "source/val/validate_primitives.cpp",
     "source/val/validate_ray_query.cpp",
     "source/val/validate_ray_tracing.cpp",
+    "source/val/validate_ray_tracing_reorder.cpp",
     "source/val/validate_scopes.cpp",
     "source/val/validate_scopes.h",
     "source/val/validate_small_type_uses.cpp",