Add semi-dynamic `ccall` support

[topolarity]

          I relaxed this test and marked the original as broken

We need to expand our resolution here to walk through the PhiNode in the LLVM IR and notice the ccall / jl_load_and_lookup machinery.

Originally posted by @topolarity in #68 (comment)

[topolarity]

This is not a soundness bug, but it does mean that some dynamic ccalls that we could statically resolve to the runtime are instead treated as DynamicDispatch