"PC" stands for "personal computer". It is a generic term that implies nothing about a specific computer's hardware or software. There are PCs that run Windows, Mac OS, many different distributions of GNU/Linux, assorted varieties of BSD, and countless other operating systems.

Certainly "Mac" is shorter than "Macintosh-branded hardware that runs Macintosh OS", but drawing a distinction between "Mac" and "PC" is inaccurate because Macs are generally a type of PC. And "for PC/Mac/Linux", as one game developer wrote, is nonsense in about five different ways.

If what you mean is "Windows", you should say "Windows". Save yourself some misunderstandings!