avoid useless conversion to set that randomizes arguments order

I admit my Python skills are pretty weak, but this set conversion
appears to be useless and it can change order of arguments from e.g.
--jobs 2 --icecream 20
to
--icecream 20 --jobs 2
As the --jobs 2 actually comes from OSC itself on multicore systems
and --icecream 20 was passed from the command line, this
obviously renders the --icecream argument rather useless.

osc/build.py

@@ -521,7 +521,7 @@ def main(opts, argv):
     if bi.release:
         buildargs.append('--release %s' % bi.release)
 
-    buildargs = ' '.join(set(buildargs))
+    buildargs = ' '.join(buildargs)
 
     # real arch of this machine
     # vs.