In the build Makefiles, this adds a function (uniq) which removes
duplicate entries from lists. We apply this to the DESIGN_SRCS passed
to the Vivado build process. This eliminates some warnings from
duplicate source files caused by redundantly referencing source files in
the Makefiles, possibly because they are listed in more than one source
file variable.
Original-commit: 1944263412d329d53b32a17e9735b79e59e319d7