patch build-gnu.sh for NixOS

util/build-gnu.sh

@@ -371,3 +371,8 @@ sed -i  "s/color_code='0;31;42'/color_code='31;42'/" tests/ls/quote-align.sh
 
 # Slightly different error message
 sed -i 's/not supported/unexpected argument/' tests/mv/mv-exchange.sh
+# Most tests check that `/usr/bin/tr` is working correctly before running.
+# However in NixOS/Nix-based distros, the tr coreutil is located somewhere in
+# /nix/store/xxxxxxxxxxxx...xxxx/bin/tr
+# We just replace the references to `/usr/bin/tr` with the result of `$(which tr)`
+sed -i  's/\/usr\/bin\/tr/$(which tr)/' tests/init.sh