make: Introduce DATAROOTDIR
make: Introduce DATAROOTDIR

This makes it easier to install binaries into an arch-dependent
directory (e.g. /usr/${host}/bin) while keeping arch-independent files
like the shell completions under /usr/share by specifying e.g.
PREFIX=/usr/${host} and DATAROOTDIR=/usr/share

uutils/coreutils,uutils/coreutils,uutils/coreutils