arch: remove ia64

ia64 is broken in every gcc/glibc combinations I tested (except for the
existing sample that used very old versions).

Nobody complained on the list about not being able to build recent versions.

So the only way forward I can see is to remove the architecture altogether.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # m68k specific configuration file

 # depends on EXPERIMENTAL

 config ARCH_m68k

     select ARCH_SUPPORTS_32

     select ARCH_DEFAULT_32

     select ARCH_DEFAULT_BE

     select ARCH_SUPPORT_CPU

      help

       The m68k architecture