libcosmicAppHook: use RUSTFLAGS instead of platform specific flags (#464981)

pkgs/by-name/li/libcosmicAppHook/libcosmic-app-hook.sh

@@ -15,7 +15,11 @@ libcosmicAppVergenHook() {
 
 libcosmicAppLinkerArgsHook() {
   # Force linking to certain libraries like libEGL, which are always dlopen()ed
-  local flags="CARGO_TARGET_@cargoLinkerVar@_RUSTFLAGS"
+  # local flags="CARGO_TARGET_@cargoLinkerVar@_RUSTFLAGS"
+
+  # Temporarily use this simpler solution, it should work for simple cross compilation
+  # https://github.com/NixOS/nixpkgs/issues/464392
+  local flags="RUSTFLAGS"
 
   export "$flags"="${!flags-} -C link-arg=-Wl,--push-state,--no-as-needed"
   # shellcheck disable=SC2043

pkgs/by-name/li/libcosmicAppHook/package.nix

@@ -55,7 +55,10 @@ makeSetupHook {
       lib.makeSearchPath "share" (
         lib.optionals includeSettings [ fallbackThemes ] ++ [ targetPackages.cosmic-icons ]
       );
-    cargoLinkerVar = targetPackages.stdenv.hostPlatform.rust.cargoEnvVarTarget;
+    # Temporarily using RUSTFLAGS: https://github.com/NixOS/nixpkgs/issues/464392
+    # See ./libcosmic-app-hook.sh
+    # cargoLinkerVar = targetPackages.stdenv.hostPlatform.rust.cargoEnvVarTarget;
+
     # force linking for all libraries that may be dlopen'd by libcosmic/iced apps
     cargoLinkLibs = lib.escapeShellArgs (
       [