Issue Description:

I guess on Darwin, the micro-architecture that Swift targets is determined by the deployment target. On Linux/Windows/... this is isn't possible however.

I think Swift should clearly specify two things:

• which Intel micro-architecture does the compiler expect as a minimum

• which Intel micro-architecture does a program compiled with the Swift compiler expect as a minimum (by default)

Also, Swift should output that in swift -version or similar.

This would've helped with bugs such as SR-14186 .