• Open Xcode
• Select File->New->New Project
• Select macOS (OS X in older versions) -> Command line tool
• Choose C as type
• Fill out the name and the other relevant wizards parts you need
• click the main.c file to select it

And you should be good to go

There is an open source project on GitHub that (quote) "provides an easy-to-use development environment for Swift programming for Windows applications": Swift for Windows.

System Requirement

• Windows 10 64bit, Windows 7 64bit

NOTE

The project was initially hosted on Microsoft CodePlex, but then moved to GitHub.

You cannot revert the entire project at once in Xcode, but you could do it from the terminal; just cd into the folder of your project and type git log to find the hash you're looking for, then do git checkout [hash].