[gn build] Port 74fd3cb

Author: llvmgnsyncbot

llvm/utils/gn/secondary/libcxx/include/BUILD.gn

@@ -246,6 +246,7 @@ if (current_toolchain == default_toolchain) {
       "__ranges/all.h",
       "__ranges/concepts.h",
       "__ranges/copyable_box.h",
+      "__ranges/dangling.h",
       "__ranges/data.h",
       "__ranges/drop_view.h",
       "__ranges/empty.h",