Add support for js-unknown-ghcjs

This adds enough logic to nixpkgs to support the `js-unknown-ghcjs` triple.

lib/systems/examples.nix

@@ -119,7 +119,7 @@ rec {
     config = "aarch64-none-elf";
     libc = "newlib";
   };
-  
+
   aarch64be-embedded = {
     config = "aarch64_be-none-elf";
     libc = "newlib";
@@ -129,12 +129,12 @@ rec {
     config = "powerpc-none-eabi";
     libc = "newlib";
   };
-  
+
   ppcle-embedded = {
     config = "powerpcle-none-eabi";
     libc = "newlib";
   };
-  
+
   alpha-embedded = {
     config = "alpha-elf";
     libc = "newlib";
@@ -212,4 +212,10 @@ rec {
     libc = "msvcrt"; # This distinguishes the mingw (non posix) toolchain
     platform = {};
   };
+
+  # Ghcjs
+  ghcjs = {
+    config = "js-unknown-ghcjs";
+    platform = {};
+  };
 }