UI: update ui/pixmap.cc to specify unistd.h include for unlink
UI: update ui/pixmap.cc to specify unistd.h include for unlink

Acked-by: Tim Janik <6ec6ff229c4e1c5bbd5933ee92e6c5832ff023bb@gnu.org>

tim-janik/rapicorn,tim-janik/rapicorn,tim-janik/rapicorn,tim-janik/rapicorn,tim-janik/rapicorn