configure.in:  fix BUILD_THREAD_FLAVORS list

Bad checks
rtai-kernel.c:  fix compile problem on 32-bit x86

ipipe.h requires a macro from include/linux/percpu-defs.h, normally
included from module.h.

rtapi.h includes module.h, so it needs to be included before rtai.h in
rtai-kernel.c.

The 64-bit compile worked because the arch-specific rtai_vectors.h
includes linux/interrupt.h, which includes module.h.  The 32-bit does
not include interrupt.h, and it does include ipipe.h, so the macro was
not defined early enough, resulting in compile error for 32-bit only.