wasmtime symlink resolution policy may be too strict

### Test Case

```c
#include
#include
#include
#include
#include

int main(int argc, char *argv[]) {
chdir(argv[1]);
if(fopen("bar", "rb") == NULL) {
perror(strerror(errno));
exit(errno);
}
}
```

### Steps to Reproduce

Use `wasi-sdk` to compile & link `foo.c` above to `foo.wasm`, then:

```
$ touch /tmp/bar
$ ln -s /tmp/bar bar
$ wasmtime run --mapdir /::/ -- foo.wasm $PWD
```

### Actual Results

The example above would fail with `Operation not permitted`. However, I've explicitly passed `--mapdir /::/` to `wasmtime`, so the entire host filesystem should be visible within the wasm module, and symlink resolution from `$PWD/bar` to `/tmp/bar` should work out of the box.

### Versions and Environment

Wasmtime version or commit: `wasmtime-cli 7.0.0`

Operating system: `Ubuntu 22.10`

Architecture: `x86_64`