feat(hermit): add stabilized interface

HermitOS is a unikernel and its interface to the kernel is provided
by https://crates.io/crates/hermit-abi. In the meantime parts of the
interface is stabilized and we want to integrated it into libc.
Unstable version will be still provided by hermit-abi.

Co-authored-by: Martin Kröning <[email protected]>
Signed-off-by: Martin Kröning <[email protected]>

Author: mkroening