`-fast-llvm` bypasses the mangler. We *could* do this if we had `-fast-llvm` *and* `-fno-plt`; however `-fno-plt` is only supported in the `clang` frontend, and essentially emits `nonlazybind` function attributes. LLVM does not guarantee that all architecture lowering backends respect that attribute and as such this would only work on `x86_64`, and on `aarch64` if passed `-aarch64-enable-nonlazybind`. Arm32 backends don't seem to support this attribute at all. Fixes #621