configure: also search for libtinfo if needed

configure: also search for libtinfo if needed

As Justin says:

    When building ncurses with --with-termlib several symbols get moved from
    libncurses.so to libtinfo.so. Thus when linking with libncurses.so, one
    additionally needs to link with libtinfo.so.

Contrary to the Linux kernel (that is on the verge of using pkg-config or
the ncurses*-config scripts), we simply see if we need to link against
libtinfo to get a symbol known to get moved there.

Reported-by: Justin <jlec@gentoo.org>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>