To use ARCH, in order to have several subdirectories for each architecture,
edit
   config/Imake.tmpl                 (for Makefiles)
   tools/camltop                     (for running the toplevel)
   tools/magic.sh                    (for running the examples)

and suppress (or comment) the lines ARCH=.

Then update the Makefiles (the command "imake" must exist on your system):
   make Makefile
   make Makefiles
