If you have GNU make available, you can use the remake.r script
to generate a Makefile and then use make to build all the files
as needed. E.g.:

    make tests

to run tests for any updated file.

How to run remake.r:

From a command line, just run:

    rebol -qws remake.r

It will ask you some questions and create a .conf file for future use.
You only have to run remake the first time to get the Makefile.
After that, the Makefile gets regenerated as needed automatically.