libcosmicAppHook: use RUSTFLAGS instead of platform specific flags

This ensures these flags are picked up correctly, after latest rust
update. We can revert this if we solve the root cause later.

See https://github.com/NixOS/nixpkgs/issues/464392

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 (
       [