[libclc] [libclc] Implement __clc_rsqrt with __ocml_rsqrt_* functions (PR #152436)

[Matt Arsenault via cfe-commits]

https://github.com/arsenm commented:

ocml rsqrt should be deleted, this is implementable by

```
float rsqrt(float x) {
    #pragma clang fp contract(fast)
    return 1.0f / __builtin_elementwise_sqrt(x);
}
```

https://github.com/llvm/llvm-project/pull/152436