WasmFS test failures

A handful of tests are failing in `wasmfs` test runner mode, that look like actual issues:

`wasmfs.test_module_stdin`
- Error: EAGAIN: resource temporarily unavailable

`wasmfs.test_statvfs`
- st.f_ffree > st.f_files, same issue than in wasmfs.test_fs_nodefs_statvfs

`wasmfs.test_fs_nodefs_statvfs`
- Assertion failed: st.f_ffree <= st.f_files && "Free inodes should not exceed total inodes"

`wasmfs.test_fs_enotdir`
- Assertion failed: open("./does-not-exist/", O_CREAT, 0777) == -1 in test_fs_enotdir.c line 20

`wasmfs.test_fs_readdir_ino_matches_stat_ino`
- Assertion failed: "a_ino == sta.st" in test_fs_readdir_ino_matches_stat_ino.c, line 58

`wasmfs.test_unistd_write_broken_link`
- Assertion failed: "r == 3" in test_unistd_write_broken_link.c line 22

`wasmfs.test_unistd_symlink_on_nodefs`
- Assertion failed: "fd" in symlink_on_nodefs.c line 62

`wasmfs.test_unistd_misc`
- fails in testing fdatasync, tcgetpgrp and pipe

Apart from these remaining failures, the `wasmfs` suite seems to be in passing condition.

Start by running the wasmfs test runner and reproducing the listed failures, especially wasmfs.test_module_stdin, wasmfs.test_statvfs, and wasmfs.test_unistd_misc. Inspect the referenced tests test_fs_enotdir.c, test_fs_readdir_ino_matches_stat_ino.c, test_unistd_write_broken_link.c, and symlink_on_nodefs.c. Done means the remaining wasmfs tests pass without regressions.

Written by the indexing model from the issue text.