[gn build] Port 08920cc0

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

@@ -467,6 +467,8 @@ if (current_toolchain == default_toolchain) {
       "__threading_support",
       "__tree",
       "__tuple",
+      "__type_traits/integral_constant.h",
+      "__type_traits/is_callable.h",
       "__undef_macros",
       "__utility/as_const.h",
       "__utility/auto_cast.h",