Because of common dependencies between the
static libraries list can contain duplicates.

We reduce these down to the single last one in
the list.

This reduces the relative time of a rebuild from:

$ (cd builddir/; time make -j)
...
real	0m30.789s
user	1m33.477s
sys	0m19.678s

and the LIB entries
$ grep ADDLIB builddir/libmysqld/mysqlserver-\$\<CONFIG\>.mri.tpl  | wc -l
179

$ du -h builddir/libmysqld/libmariadbd.a
4.1G	builddir/libmysqld/libmariadbd.a

To:

$ (cd builddir/; time make -j)
...
real	0m20.139s
user	1m32.423s
sys	0m12.208s

$ grep ADDLIB builddir/libmysqld/mysqlserver-\$\<CONFIG\>.mri.tpl  | wc -l
25

$ du -h builddir/libmysqld/libmariadbd.a
688M	builddir/libmysqld/libmariadbd.a