Merge #414 #422

414: Targets: Use none-elf instead of hermit llvm-target r=stlankes a=mkroening

As discussed in https://github.com/hermitcore/rusty-hermit/issues/197#issuecomment-999379314

, this way the kernel's `libhermit.a` has `OS/ABI: UNIX - System V` and the resulting application has `OS/ABI: <unknown: ff>`. This works for the Rust-toolchain as well as the C-toolchain.

422: Condvar: Mark sys functions as extern "C" r=stlankes a=mkroening

They are declared in hermit-abi as extern "C" already.
So the current definition without extern "C" is wrong.

Co-authored-by: Martin Kröning <mkroening@posteo.net>
Co-authored-by: Martin Kröning <m.kroening@hotmail.de>