coop-threads: Pthread primitives change ABI when coop threading is enabled

[alexcrichton]

For wasm32-wasip3 the public ABI of the pthread_* primitives (e.g. mutex/condvar/rwlock/etc) currently change with -DENABLE_COOP_THREADS=ON. This'll make the bindings story for languages like Rust more difficult in the wasip3 world and is, I believe, ideally something we should avoid. In talking with @TartanLlama about this what I'm thinking we might be able to do here is:

• Unconditionally, for all wasi targets, compile the wasi-threads primitives for mutexes/condvars/etc
• Have a #ifdef'd implementation for a futex-style API
  • On wasip1/2/3 w/o threads this just returns an error/panics/traps/etc on blocking
  • On wasi-threads it does memory.atomic.*
  • On coop threads it does __waitlist_node or what's there today
• This additionally paves the way to exporting a futex-style API from wasi-libc itself for other languages like Rust to use

[alexcrichton]

Fixed in #827