Add perl to all shell environments (#235)

GHC's test suite requires `perl` (e.g. the testsuite driver and various
test scripts). Like `which`, `perl` is not part of stdenv's initialPath
and was only reachable via the host system before the hermetic PATH
change. Add it explicitly to all four shell definitions.

Author: angerman

cross-js.nix

@@ -100,6 +100,7 @@ pkgs.mkShell ({
         (pkgs.pkg-config or pkgconfig)
         (tool "happy")
         (tool "alex")
+        perl
         stdenv.cc.cc.lib
         which
     ]) ++ (with pkgs.buildPackages; [

cross-windows.nix

@@ -205,6 +205,7 @@ pkgs.pkgsBuildBuild.mkShell ({
         (pkgsBuildBuild.pkg-config or pkgsBuildBuild.pkgconfig)
         (tool "happy")
         (tool "alex")
+        pkgsBuildBuild.perl
         stdenv.cc.cc.lib
         pkgsBuildBuild.which
     ])

dynamic.nix

@@ -120,6 +120,7 @@ pkgs.mkShell {
       ]
       ++ (with pkgs; [
         openssl
+        perl
         pcre
         pkg-config
         which

static.nix

@@ -158,6 +158,7 @@ pkgs.mkShell (rec {
         (compiler.override { enableShared = true; })
     ] ++ (with pkgs; [
         (pkgs.pkg-config or pkgconfig)
+        perl
         stdenv.cc.cc.lib
         which
     ]) ++ (with pkgs.buildPackages; [