multimedia/ffmpeg: restore -L${LOCALBASE}/lib after r428893

ld.bfd from devel/binutils by default looks under LOCALBASE/lib. If we
revert to ld.bfd (or even ld.lld) from base the following would happen.

===>  Configuring for ffmpeg-3.2.2_2,1
ERROR: gmp not found

Submitted by: marino