Compilation on hermit fails because of missing libc components

[m-mueller678]

Building for target x86_64-unknown-hermit fails because these are missing:

libc::MAP_ANON
libc::MAP_FAILED
libc::MAP_PRIVATE
libc::mmap
libc::mprotect
libc::munmap
libc::PROT_NONE
libc::PROT_WRITE
libc::_SC_PAGE_SIZE

[m-mueller678]

I have prepared a commit to treat hermit like wasm32, though I have not tested it yet. Depending on how it works out, I will open a pull request later.

9cff7c6