dialog: fix build failure

The old ncurses trick is no longer needed for this version, in fact it's
harmful. Switch to proper configure options.
Also disable rpath hackery since it's not required and could be
problematic. Fixes:
http://autobuild.buildroot.net/results/411/411f6171e972eab4486143dedbfd078136886ab0/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>