boost: Reduce noise during cross compile.

I guess the "set -x" was only left there for debugging, so I'm removing
it because it let's the scrollback buffer explode ;-)

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/development/libraries/boost/generic.nix

@@ -173,7 +173,6 @@ stdenv.mkDerivation {
     # usual --build and --host added on cross building.
     preConfigure = ''
       export configureFlags="--without-icu ${concatStringsSep " " commonConfigureFlags}"
-      set -x
       cat << EOF > user-config.jam
       using gcc : cross : $crossConfig-g++ ;
       EOF