ncurses: enable shared library build on the host

On the host, we generally build and install a shared library rather
than a static version of libraries. In this specific case, we will
want to build host-gettext, which builds a shared library that depends
on ncurses. And this doesn't work well if ncurses is static because it
hasn't been built with -fPIC. Therefore, let's build ncurses as shared
on the host.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>