configure: add make flag and define for ARCH_X86_64 for all OSes

[melted] / demo / mlt_watermark

inigo \
clip2.dv out=1000 \
-track \
watermark1.png out=1000 \
-transition composite fill=1 in=0 out=1000 a_track=0 b_track=1 geometry=85%,5%:10%x10% \
$*