linuxManualConfig: set badPlatforms

Older kernels shouldn't be marked as supporting architectures that
were only added to the kernel later.

pkgs/os-specific/linux/kernel/manual-config.nix

@@ -352,6 +352,9 @@ let
           maintainers.thoughtpolice
         ];
         platforms = platforms.linux;
+        badPlatforms =
+          lib.optionals (lib.versionOlder version "4.15") [ "riscv32-linux" "riscv64-linux" ] ++
+          lib.optional (lib.versionOlder version "5.19") "loongarch64-linux";
         timeout = 14400; # 4 hours
       } // extraMeta;
     };