This commit affects ELF kernels only.

This commit affects ELF kernels only.

Remove "setdefs.h" and arrange to generate it automatically at
ELF kernel build time.

"gensetdefs.c" is a utility which scans a set of ELF object files
and outputs a line ``DEFINE_SET(name, length);'' for each linker
set that it finds.  When generating an ELF kernel, this is run just
before the final link to generate "setdefs.h".

Remove the init_sets() function from "setdef0.c", and its call from
"machdep.c".  Since "gensetdefs.c" calculates the length of each
set, it is no longer necessary in an ELF kernel to count the set
elements at kernel initialization time.  Also remove "set_of_sets"
which was used for this purpose.

Link "setdef0" and "setdef1" into the kernel only if building for
ELF.  Since init_sets() is no longer used, there is no need to link
them into an a.out kernel.