[gn build] Port bf20a09

Author: llvmgnsyncbot

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

@@ -173,8 +173,11 @@ if (current_toolchain == default_toolchain) {
       "__chrono/system_clock.h",
       "__chrono/time_point.h",
       "__compare/common_comparison_category.h",
+      "__compare/compare_partial_order_fallback.h",
+      "__compare/compare_strong_order_fallback.h",
       "__compare/compare_three_way.h",
       "__compare/compare_three_way_result.h",
+      "__compare/compare_weak_order_fallback.h",
       "__compare/is_eq.h",
       "__compare/ordering.h",
       "__compare/partial_order.h",