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.  If Elk is going to be compiled with an option that sets the data
segment origin (such as -Wl,-D,800000), you have to use the same option
when compiling pchb.c.

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.
