process: fix execPath detection and spawnSync pipe shutdown

[artemyarulin]

• use uv_exepath() for process.execPath, with argv0 fallback
• ignore UV_EACCES from spawnSync() stdin shutdown on WASIX

After moving subprocesses onto the WASIX spawn model, spawnSync() could still return a successful child result while attaching an EACCES error from pipe shutdown cleanup. process.execPath also needed to follow the Node-style uv_exepath() path.

Depends on wasix-org/libuv#1 I've updated the project to look to the fixed libuv branch

With libuv fix and this PR process.execPath works, spawnSync(process.execPath, ['-e', ...]) works as well and lib test for cross-spawn now doesn't stall anymore

[theduke]

Should we maybe just fix the EACCESS thing in wasix?

[artemyarulin]

Should we maybe just fix the EACCESS thing in wasix?

Probably the right fix would be actually again in libuv: Fix stream.c so uv_shutdown does not call shutdown(SHUT_WR) on stdin pipes created by WASIX spawn, because those are plain pipes, not sockets.