This was quite brittle and has now been superseded
by swift-xcodegen. Remove the CMake/build-script
logic for it, leaving the option behind to inform
users to switch to using xcodegen instead.
Generate a new 'SwiftRuntimes' xcodeproj if a build directory
for 'Runtimes' is specified with `--runtimes-build-dir`, along with a
combined 'Swift+Runtimes' workspace.
This enables the use of folder references for
compatible targets, allowing new source files to
be added without needing to regenerate the project.
Currently disabled by default; I'd like to get
some living-on before enabling.
This is a tool specifically designed to generate
Xcode projects for the Swift repo (as well as a
couple of adjacent repos such as LLVM and Clang).
It aims to provide a much more user-friendly experience
than the CMake Xcode generation (`build-script --xcode`).
