Draft: Split out aws-sdk-cpp-core, aws-sdk-cpp-iam, and aws-sdk-cpp-s3

A first step towards fully splitting aws-sdk-cpp into modular packages. This should be just enough for arrow#1

This was based on an analysis of the dependency graph between /usr/lib/libaws-cpp-sdk-* which looks like this:

I don't have a very good graph visualization yet, but basically you can see that pretty much everything depends on libaws-crt-cpp.so and libaws-cpp-sdk-core.so, most libs don't have any other dependency and a few depend on something else additionally.

The splitting could go as deep as you want but the PKGBUILD will not scale to hundreds of split packages 😄 But we could at least split these high-level parts of the SDK (as opposed to the generated parts).