buildroot

coreutils: use the new gettext logic

This commit uses TARGET_NLS_DEPENDENCIES instead of existing logic to
add the dependency on gettext. To keep the existing behavior, we keep
the --with-libintl-prefix option, but only when a libintl library is
effectively provided by gettext.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>