The problem comes in as soon as you need conditionals, which is likely when attempting to build something portably. There may be some gymnastics that can be done to write around the lack of their presence in standard make, but otherwise your options are:
- Supply multiple makefiles targeting different implementations
- Bring in autotools in all its glory (at this point you are depending on an external GNU package anyway)
- Or explicitly target GNU Make, which is the default make on Linux and macOS, is very commonly used on *BSD, and is almost certainly portable to every platform your software is going to be tested and run on. The downside being that BSD users need a heads up before typing "make" to build your software. But speaking as a former FreeBSD user, this is pretty easy to figure out after your first time seeing the flood of syntax errors.
- Supply multiple makefiles targeting different implementations
- Bring in autotools in all its glory (at this point you are depending on an external GNU package anyway)
- Or explicitly target GNU Make, which is the default make on Linux and macOS, is very commonly used on *BSD, and is almost certainly portable to every platform your software is going to be tested and run on. The downside being that BSD users need a heads up before typing "make" to build your software. But speaking as a former FreeBSD user, this is pretty easy to figure out after your first time seeing the flood of syntax errors.