ncurses: speed up the build by not installing manpages

The installation of manpages during the installation step of
host-ncurses and ncurses is horribly slow, and useless. This commit
therefore disables the installation of those manpages, using the
--without-manpages configuration option.

It brings the combined host-ncurses+ncurses configure/build/install
time from 3 minutes and 18 seconds to 1 minute and 36 seconds.

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