clock() function in ctime always return 0

### Test Case

```cpp
#include
#include

int main() {
clock_t time = clock();
printf("%ld\n", time);
}
```

### Steps to Reproduce

* Use wasi-sdk to compile.
* Use wasmtime run the WASM module.

### Expected Results

The clock tick after the module start to run.

### Actual Results

0

### Versions and Environment

Wasmtime version or commit: 0.28

Operating system: macOS 12.1 & Ubuntu 20.04

Architecture: x86_64