gdb: force to use ncurses and not termcap for host-gdb

gdb: force to use ncurses and not termcap for host-gdb

Both our target and host gdb depend on ncurses (host-ncurses for
host-gdb, of course). However, while for the target we passs
--with-curses, we are not doing this for the host variant. Due to
this, host-gdb default to using the termcap library: if such a library
is available on the build system, it will be used instead of the
host-ncurses we have built. This causes the host gdb binary to depend
on a library that we do not provide in $(HOST_DIR), breaking the
principle of a standalone SDK (which should only depend on the C
library).

To solve this, we simply pass --with-curses in HOST_GDB_CONF_OPTS,
which forces host-gdb to use the host-ncurses library.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>