Created by: robbertvanginkel
There's a flag modular on apple_library that previously set some flags different so Xcode would correctly generate modular frameworks. In Xcode 9 there's also support for static swift libraries, which we want to support in buck. Unfortunately Xcode doesn't support modular static libraries by setting some Xcode config flags, so buck will have to generate the required modulemaps during project generation.
To support this we should make use of the modular flag. This PR changes the use of the modular flag so that it can be used for both modular frameworks as well as static libraries.