HALFARSED enable toggling promptless kconfig symbols

Some kernel config symbols we need to enable in some configurations
don't have a "prompt" entry in the Kconfig files, meaning that
make oldconfig (or any other make fooconfig) won't change them.
So we add a Kconfig.local where they can be selected

In this patch we hardcode the required symbol. Next step would be
to generalise so that they could be specified in something like a
config.kernel.hiddenConfig attrset

devices/gl-ar750.nix

@@ -25,6 +25,9 @@
       "MIPS_ELF_APPENDED_DTB" = "y";
       OF = "y";
       USE_OF = "y";
+      ATH79 = "y";
+      SOC_QCA955X = "y";        #  actually QCA9531, is this even right?
+      LIMINIX = "y";
       SERIAL_8250_CONSOLE = "y";
       SERIAL_8250 = "y";
       SERIAL_CORE_CONSOLE = "y";

kernel/default.nix

@@ -25,7 +25,8 @@ let
   tree = stdenvNoCC.mkDerivation {
     name = "spindled-kernel-tree";
     src = source;
-    phases = [ "unpackPhase" "patchScripts" "installPhase" ];
+    phases = [ "unpackPhase" "patchPhase" "patchScripts" "installPhase" ];
+    patches = [ ./random.patch ];
     patchScripts = ''
       patchShebangs scripts/
     '';

kernel/random.patch

@@ -0,0 +1,9 @@
+diff --git a/Kconfig b/Kconfig
+index 745bc773f567..24a6ea92ee19 100644
+--- a/Kconfig
++++ b/Kconfig
+@@ -30,3 +30,4 @@ source "lib/Kconfig"
+ source "lib/Kconfig.debug"
+ 
+ source "Documentation/Kconfig"
++source "Kconfig.local"

kernel/vmlinux.nix

@@ -16,6 +16,17 @@ let writeConfig = name : config: writeText name
             config
           ));
     kconfigFile = writeConfig "kconfig" (config // checkedConfig);
+    # KLUDGE FIXME. some symbols we need to enable in some configurations don't
+    # have a prompt (!), so we can't turn them on just by adding FOO=y  and make oldconfig
+    #
+    # (!) yes, that was my reaction too
+    kconfigLocal = writeText "Kconfig.local" ''
+      config LIMINIX
+             prompt "Local symbols"
+             bool
+             default y
+             select SOC_QCA955X
+    '';
     checkedConfigFile = writeConfig "checked_kconfig" checkedConfig ;
     inherit lib; in
 stdenv.mkDerivation rec {
@@ -60,6 +71,7 @@ stdenv.mkDerivation rec {
     export KBUILD_OUTPUT=`pwd`
     cp ${kconfigFile} .config
     cp ${kconfigFile} .config.orig
+    cp ${kconfigLocal} Kconfig.local
     ( cd ${tree} && make V=1 olddefconfig )
   '';