[gn build] Port f5960c1

Author: aeubanks

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

@@ -807,6 +807,7 @@ if (current_toolchain == default_toolchain) {
       "__type_traits/datasizeof.h",
       "__type_traits/decay.h",
       "__type_traits/dependent_type.h",
+      "__type_traits/desugars_to.h",
       "__type_traits/disjunction.h",
       "__type_traits/enable_if.h",
       "__type_traits/extent.h",
@@ -891,7 +892,6 @@ if (current_toolchain == default_toolchain) {
       "__type_traits/nat.h",
       "__type_traits/negation.h",
       "__type_traits/noexcept_move_assign_container.h",
-      "__type_traits/operation_traits.h",
       "__type_traits/promote.h",
       "__type_traits/rank.h",
       "__type_traits/remove_all_extents.h",