[gn build] Port 69b54c1

Author: llvmgnsyncbot

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

@@ -145,6 +145,7 @@ if (current_toolchain == default_toolchain) {
       "__algorithm/prev_permutation.h",
       "__algorithm/pstl.h",
       "__algorithm/push_heap.h",
+      "__algorithm/radix_sort.h",
       "__algorithm/ranges_adjacent_find.h",
       "__algorithm/ranges_all_of.h",
       "__algorithm/ranges_any_of.h",