The -m switch doesn't cause Build to actually do anything. It causes it to only print what it might do:

% ./Build -m
Configuration: os=SunOS, rel=4.1.4, rbase=4, rroot=4.1, arch=sun4, sfx=
Using M4=/usr/5bin/m4
Will run in virgin obj.SunOS.4.1.4.sun4 using ../BuildTools/OS/SunOS

This switch is useful for determining if the Build process will recognize your machine architecture and operating system. If it does not, it will print an error such as this:

Configuration: os=EX/Unix, rel=0.1, rbase=0, rroot=0.1, arch=sun4, sfx=
Cannot determine how to support sun4.EX/Unix.0.1

Here, an experimental kernel (EX/Unix) running on a Sun4 machine turned out to be a version of Unix that Build did not understand.

We offer a complete listing of #define macros in Appendix A. Those macros, as well as much of the tuning that we discuss in Chapter 4, can be germane to porting. But be forewarned that porting sendmail and its companion programs to new operating systems is beyond the scope of this book.