I'm using Xcode 10.1. Even when using the search function in my target's Build Settings, I can't find a "Metal Compiler" or anything related Metal.
Described here, there are Metal settings that can be set in Build Settings, but there's nothing I can find: https://developer.apple.com/documentation/coreimage/cikernel/2880194-init
Has it been cut out or replaced?
You must have at least one Metal source file (which usually has a .metal extension) in the Compile Sources build phase of your selected target in order for Metal compiler settings to appear.