ncurses: Enable rpath to run the binaries using the proper libraries

With rpath the dynamic linker will properly use the libraries from
$(prefix)/lib. Otherwise it will use the system libraries which might
not be compatible or exist at all.

Change-Id: I2efa899326e75f296358d665eb2ae5778ae18611
Signed-off-by: Alban Bedel <alban.bedel@avionic-design.de>
Reviewed-on: http://review.adnet.avionic-design.de/1352
Reviewed-by: Bert van Hall <bert.vanhall@avionic-design.de>