Allow overriding perlPackages

__overrides is the worst.

Signed-off-by: Shea Levy <shea@shealevy.com>

pkgs/top-level/all-packages.nix

@@ -5252,6 +5252,7 @@ let
 
   perlPackages = recurseIntoAttrs (import ./perl-packages.nix {
     inherit pkgs;
+    __overrides = (config.perlPackageOverrides or (p: {})) pkgs;
   });
 
   perl510Packages = import ./perl-packages.nix {

pkgs/top-level/perl-packages.nix

@@ -5,12 +5,14 @@
    for each package in a separate file: the call to the function would
    be almost as must code as the function itself. */
 
-{pkgs}:
+{pkgs, __overrides}:
 
 rec {
 
   inherit (pkgs) buildPerlPackage fetchurl stdenv perl fetchsvn;
 
+  inherit __overrides;
+
   # Helper functions for packages that use Module::Build to build.
   buildPerlModule = { buildInputs ? [], ... } @ args:
     buildPerlPackage (args // {