libtorrent: fix cross-compilation

The configure script for libtorrent will attempt to compile and run a
small program during the build, which won't work when we are building
with a compiler that produces a program that won't run natively on the
build platform.

pkgs/by-name/li/libtorrent/package.nix

@@ -38,6 +38,8 @@ stdenv.mkDerivation rec {
     zlib
   ];
 
+  configureFlags = [ "--enable-aligned=yes" ];
+
   passthru.updateScript = gitUpdater { rev-prefix = "v"; };
 
   enableParallelBuilding = true;