treewide platform checks: abort -> throw

They aren't meant to be critical (uncatchable) errors.
Tested with nix-env + checkMeta:
[ "x86_64-linux" "i686-linux" "x86_64-darwin" "aarch64-linux" ]

pkgs/misc/cups/drivers/cnijfilter_4_00/default.nix

@@ -9,7 +9,7 @@
 let arch = 
   if stdenv.system == "x86_64-linux" then "64"
     else if stdenv.system == "i686-linux" then "32"
-    else abort "Unsupported architecture";
+    else throw "Unsupported system ${stdenv.system}";
 
 in stdenv.mkDerivation rec {
   name = "cnijfilter-${version}";

pkgs/misc/cups/drivers/kyocera/default.nix

@@ -4,7 +4,7 @@ let
   platform =
     if stdenv.system == "x86_64-linux" then "64bit"
     else if stdenv.system == "i686-linux" then "32bit"
-         else abort "Unsupported platform";
+         else throw "Unsupported system: ${stdenv.system}";
 
   libPath = lib.makeLibraryPath [ cups ];
 in