edk2-uefi-shell: move env variable(s) into env for structuredAttrs

pkgs/by-name/ed/edk2-uefi-shell/package.nix

@@ -23,16 +23,17 @@ edk2.mkDerivation "ShellPkg/ShellPkg.dsc" (finalAttrs: {
   ];
   strictDeps = true;
 
-  env.NIX_CFLAGS_COMPILE = toString (
-    lib.optionals stdenv.cc.isClang [
+  env = {
+    # Set explicitly to use Python 3 from nixpkgs. Otherwise, the build system will detect and try to
+    # use `/usr/bin/python3` on Darwin when sandboxing is disabled.
+    PYTHON_COMMAND = "${lib.getBin pkgsBuildHost.python3}/bin/python3";
+  }
+  // lib.optionalAttrs stdenv.cc.isClang {
+    NIX_CFLAGS_COMPILE = toString [
       "-fno-pic"
       "-Qunused-arguments"
-    ]
-  );
-
-  # Set explicitly to use Python 3 from nixpkgs. Otherwise, the build system will detect and try to
-  # use `/usr/bin/python3` on Darwin when sandboxing is disabled.
-  PYTHON_COMMAND = "${lib.getBin pkgsBuildHost.python3}/bin/python3";
+    ];
+  };
 
   # We only have a .efi file in $out which shouldn't be patched or stripped
   dontPatchELF = true;