de-duplicate QMAKE_DEFAULT_LIBDIRS after all

but this time without reshuffling it. it's actually easy with awk.

this makes the resulting qconfig.pri cleaner (and thus easier to debug).
and configure needs a few millisecs less to finish. ^^

QMAKE_DEFAULT_INCDIRS doesn't appear to contain dupes to start with.

Change-Id: I9eed2cf853cd15d0d24a885b1c3d69f22ffafb36
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

configure

@@ -3070,7 +3070,10 @@ $1 == "LIBRARY_PATH" {
     print "DEFAULT_LIBDIRS=\"";
     for (lib in library_paths) {
         dir = normalize(library_paths[lib]);
-        print quote(dir) " ";
+        if (!(dir in dirs)) {
+            print quote(dir) " ";
+            dirs[dir] = 1;
+        }
     }
     print "\"\n"
 }