atop: fix cross-compilation

atop 2.10 broke cross-compilation by hard-coding a build architecture
pkg-config. atop 2.11 fixed the issue by reading the PKG_CONFIG
environment variable, but cross-compilation remained broken in nixpkgs
because PKG_CONFIG was not set. Moving pkg-config to nativeBuildInputs
fixes the variable and the build.

pkgs/by-name/at/atop/package.nix

@@ -22,7 +22,9 @@ stdenv.mkDerivation rec {
     hash = "sha256-m5TGZmAu//e/QC7M5wbDR/OMOctjSY+dOWJoYeVkbiA=";
   };
 
-  nativeBuildInputs = lib.optionals withAtopgpu [
+  nativeBuildInputs = [
+    pkg-config
+  ] ++ lib.optionals withAtopgpu [
     python3.pkgs.wrapPython
   ];
 
@@ -30,7 +32,6 @@ stdenv.mkDerivation rec {
     glib
     zlib
     ncurses
-    pkg-config
   ] ++ lib.optionals withAtopgpu [
     python3
   ];