Bug#1003009: notcurses FTBFS: notcurses-ffi exists in debian/tmp but is not installed to anywhere

[nick black]

reopen 1003009

i added -DBUILD_FFI_LIBRARY=off with the intention of no longer
building these three shared objects. looking at it now, however,
this CMake variable doesn't actually seem to guard their
building and installation, and thus it will not have the desired
effect. i'm fixing this upstream, and will build a -3 with the
necessary patch. sigh.