If you are writing a "config/system" file for a new architecture, compile
and run the program pchb.c to see if pointer_constant_high_bits needs to
be set.

Also, you may want to compile and run alloca.c to check if your
system's alloca() function is usable for Elk.  See the leading comment
in alloca.c.

sgihack.c may be required on SGI workstations; see ../MACHINES.
