The fetchDependencies script puts build files in External/build directory.
Xcode puts build files in standard Library/.../DerivedData directory.
Copy compiled external static library files to External/build/iOS &
External/build/macOS regardless of location of intermediates.
Add separate ExternalDependencies Xcode project.
Move external dependencies to ExternalDependencies project.
The fetchDependencies script builds external dependencies libraries into External/build.
The fetchDependencies script prepares SPIRV-Tools without preparing glslang.
MoltenVK links to pre-built external dependency static libraries.
MoltenVK includes external library headers using full relative paths.