If SwiftLint is built from this state using the Swift SDK, we'll get a
large self-contained Linux executable that runs without loading SourceKit.
It can do that by disabling any rule that requires SourceKit.
With `SWIFTLINT_DISABLE_SOURCEKIT` set on a normally (dynamically linked)
binary, the behavior is the same. That's different from the previously
reported more serious warnings.
These macros remove some of the boilerplate involved when writing rules.
This change also adds test infrastructure for the macros used within
SwiftLint.
Danny Mösch
JP Simard