Add fetchGitMirror function

overlay.nix

@@ -105,14 +105,14 @@ let
 
   # Native build in that platform doesn't imply cross build works
   canCrossCompile = platform: default: pkg:
-    (isDerivation pkg) &&
+    (lib.isDerivation pkg) &&
     # If meta.cross is undefined, use default
     (pkg.meta.cross or default) &&
-    (meta.availableOn final.pkgsCross.${platform}.stdenv.hostPlatform pkg);
+    (lib.meta.availableOn final.pkgsCross.${platform}.stdenv.hostPlatform pkg);
 
   # For now only RISC-V
-  crossSet = genAttrs [ "riscv64" ] (platform:
+  crossSet = lib.genAttrs [ "riscv64" ] (platform:
-    filterAttrs (_: canCrossCompile platform true)
+    lib.filterAttrs (_: canCrossCompile platform true)
       final.pkgsCross.${platform}.bsc.pkgsTopLevel);
 
   buildList = name: paths:
@@ -132,7 +132,7 @@ let
   allList = buildList' "ci-all" [ pkgsList testsList ];
   # For now only RISC-V
   crossList = buildList "ci-cross"
-    (filter
+    (lib.filter
       (canCrossCompile "riscv64" false) # opt-in (pkgs with: meta.cross = true)
         (builtins.attrValues crossSet.riscv64));