The LIBS statement generated into Makefiles contained duplicate
libraries when application was linking static libraries.
Fixed by adapting the logic from unixmake.cpp's version of
processPrlFiles() to remove duplicates.
Change-Id: I12e152900233d0376b7d7ac6cd18a92850a6d640
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>