ruby: fix host build breakage

When building host-ruby with ncurses enabled on an x86_64 host we get a
"relocation R_X86_64_32 against `_nc_globals' can not be used when making
a shared object; recompile with -fPIC" error when building.
Just disable ncurses and readline support for the host version - we
don't need it.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>