We use boost too. To simplify its inclusion into new applications I have created a Xcode project you can drop into your workspace to include boost. It is based on a Makefile so you need the Xcode commandline tools installed.
The project is here https://github.com/Cogosense/iOSBoostFramework.
Clone the project into your workspace, then click on Menu File->"Add Files to workspace". Select iOSBoostFramework/iOSBoostFramework.xcodeproj in the file finder and click add.
The Makefile in the iOSBoostFramework directory controls what is built and how it is built. There is support for Xcode workspace dependencies, bitcode generation, and only the target architectures selected by Xcode are built.
The following libraries are built test, thread, atomic, signals, filesystem, regex, program_options, system date_time, serialization, exception, locale, and random.
All the separate libraries and architectures are combined, the final build output is a FAT boost.framework Framework bundle which can be linked into the application.
The version of boost is specified in the Makefile (currently 1.64.0), it is downloaded, built for all active architectures and installed in the BUILT_PRODUCTS_DIR specified by xcode.