Not sure three way merge is the correct terminology, so I will describe the capability.
Assume you're working on an MCU board library repository Raspberry PI B containing a file RPIB.h containing its pinouts and other definitions. A year later, a new MCU board is released called Raspberry PI B+. It is identical except its pinout is slightly different. As a result, you clone RPIB.h, renumber a few pins and name the file as RPIB+.h.
Is it possible for Git to track RPIB+.h and RPIB.h and apply changes to both? For instance, a bugfix in either file is merged into the other? This would make it difficult to forget applying the bugfix to both.