treewide: Remove stdenv.isCross

I *want* cross-specific overrides to be verbose, so I rather not have
this shorthand. This makes the syntactic overhead more proportional to
the maintainence cost. Hopefully this pushes people towards fewer
conditionals and more abstractions.

pkgs/development/libraries/libgcrypt/default.nix

@@ -30,7 +30,7 @@ stdenv.mkDerivation rec {
     ++ stdenv.lib.optional stdenv.isDarwin gettext
     ++ stdenv.lib.optional enableCapabilities libcap;
 
-  preConfigure = stdenv.lib.optionalString stdenv.isCross ''
+  preConfigure = stdenv.lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''
     # This is intentional: gpg-error-config is a shell script that will work during the build
     mkdir -p "$NIX_BUILD_TOP"/bin
     ln -s ${libgpgerror.dev}/bin/gpg-error-config "$NIX_BUILD_TOP/bin"