tmux: add utf8proc on Darwin

Without utf8proc, tmux on Darwin does not get enough information about character
widths. This means that tmux has rendering issues involving multi-byte
characters like emoji, ending up with visual artifacts.

pkgs/tools/misc/tmux/default.nix

@@ -6,6 +6,7 @@
 , bison
 , ncurses
 , libevent
+, utf8proc
 }:
 
 let
@@ -49,12 +50,12 @@ stdenv.mkDerivation rec {
   buildInputs = [
     ncurses
     libevent
-  ];
+  ] ++ lib.optionals stdenv.isDarwin [ utf8proc ];
 
   configureFlags = [
     "--sysconfdir=/etc"
     "--localstatedir=/var"
-  ];
+  ] ++ lib.optionals stdenv.isDarwin [ "--enable-utf8proc" ];
 
   enableParallelBuilding = true;