bpython: substituteAll the path to which

This is used to detect the presence of xclip and other clipboard
handling tools.

Fixes https://github.com/NixOS/nixpkgs/issues/56941.

pkgs/development/python-modules/bpython/clipboard-make-which-substitutable.patch

@@ -0,0 +1,27 @@
+From 6f544a5bd43446859754cb80e012af933b843db9 Mon Sep 17 00:00:00 2001
+From: Florian Klink <flokli@flokli.de>
+Date: Wed, 3 Jun 2020 22:05:34 +0200
+Subject: [PATCH] clipboard: make which substitutable
+
+This is used to detect the presence of xclip and other clipboard
+handling tools.
+---
+ bpython/clipboard.py | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/bpython/clipboard.py b/bpython/clipboard.py
+index aee429b..f346429 100644
+--- a/bpython/clipboard.py
++++ b/bpython/clipboard.py
+@@ -58,7 +58,7 @@ class OSXClipboard(object):
+ 
+ def command_exists(command):
+     process = subprocess.Popen(
+-        ["which", command], stderr=subprocess.STDOUT, stdout=subprocess.PIPE
++        ["@which@", command], stderr=subprocess.STDOUT, stdout=subprocess.PIPE
+     )
+     process.communicate()
+ 
+-- 
+2.26.2
+