buildroot

ncurses: fix build failure with ncurses 6.1

Ncurses 6.1 introduced the config option --disable-stripping which is
set to no by default.

Set this option to ensure that ncurses doesn't try to strip the
executables.

Fixes:

  http://autobuild.buildroot.net/results/3a5ddfcf7cd3a5c2bc068e3e33c823d6bcd3e79b

Signed-off-by: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>