There may be some features configure cannot figure out automatically, but needs to determine by the type of machine the package will run on. Usually, assuming the package is built to be run on the same architectures, configure can figure that out, but if it prints a message saying it cannot guess the machine type, give it the --build=type option. type can either be a short name for the system type, such as ‘sun4’, or a canonical name which has the form:
cpu-company-system
where system can have one of these forms:
os
kernel-os
See the file config.sub for the possible values of each field. If config.sub isn't included in this package, then this package doesn't need to know the machine type.
If you are building compiler tools for cross-compiling, you should use the option --target=type to select the type of system they will produce code for.
If you want to use a cross compiler, that generates code for a platform different from the build platform, you should specify the host platform (i.e., that on which the generated programs will eventually be run) with --host=type.