No matching signing identity found "Mac Developer:"

Self-Signed Codesign Certificate

It's really simple to fix this; you can create your own self-signed codesign certificate in Keychain Access. If you decide to distribute your app later, or want it to behave nicely with Gatekeeper then you'll of course need to join the Mac Developer Program.

*If it's primarily for your own usage though then you can likely choose not to codesign it at all.

Self-signed codesiging and No codesigning in XCode

Xcode Version 9.2

Build Settings -> Code Signing Identity -> Don't Code Sign