systems/parse.nix: support weird system configs

There are some weird ones out there that don’t follow any pattern:

- arm-none-eabi
- powerpc-none-eabi
- aarch64-none-elf

lib/systems/parse.nix

@@ -119,6 +119,7 @@ rec {
     apple = {};
     pc = {};
 
+    none = {};
     unknown = {};
   };
 
@@ -202,6 +203,7 @@ rec {
     cygnus       = {};
     msvc         = {};
     eabi         = {};
+    elf         = {};
 
     androideabi  = {};
     android      = {
@@ -263,6 +265,8 @@ rec {
     "2" = # We only do 2-part hacks for things Nix already supports
       if elemAt l 1 == "cygwin"
         then { cpu = elemAt l 0;                      kernel = "windows";  abi = "cygnus";   }
+      else if (elemAt l 1 == "eabi")
+        then { cpu = elemAt l 0; vendor = "none"; kernel = "none"; abi = elemAt l 1; }
       else   { cpu = elemAt l 0;                      kernel = elemAt l 1;                   };
     "3" = # Awkwards hacks, beware!
       if elemAt l 1 == "apple"
@@ -273,6 +277,10 @@ rec {
         then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "windows";  abi = "gnu"; }
       else if hasPrefix "netbsd" (elemAt l 2)
         then { cpu = elemAt l 0; vendor = elemAt l 1;    kernel = elemAt l 2;                }
+      else if (elemAt l 2 == "eabi")
+        then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "none"; abi = elemAt l 2; }
+      else if (elemAt l 2 == "elf")
+        then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "none"; abi = elemAt l 2; }
       else throw "Target specification with 3 components is ambiguous";
     "4" =    { cpu = elemAt l 0; vendor = elemAt l 1; kernel = elemAt l 2; abi = elemAt l 3; };
   }.${toString (length l)}