package/xterm: compile with libXft support when it selected

When libXft (FreeType) library is selected, xterm will use it.
host-pkgcong is used to search for libXft during configure, so it
is in the dependencies.

Signed-off-by: Mikhail Peselnik <bas@bmail.ru>
Reviewed-by: Romain Naour <romain.naour@openwide.fr>
Tested-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>