Earlier we discussed the standard option -b which chooses among different installed compilers for completely different target machines, such as VAX vs. 68000 vs. 80386.
In addition, each of these target machine types can have its own special options, starting with -m, to choose among various hardware models or configurations—for example, 68010 vs 68020, floating coprocessor or none. A single installed version of the compiler can compile for any model or configuration, according to the options specified.
Some configurations of the compiler also support additional special options, usually for compatibility with other compilers on the same platform.
These options are defined by the macro TARGET_SWITCHES in the
machine description. The default for the options is also defined by
that macro, which enables you to change the defaults.