[libclc] [libclc] Move rsqrt to the CLC library (PR #129045)

[Matt Arsenault via cfe-commits]

================
@@ -0,0 +1,4 @@
+__attribute__((weak)) _CLC_OVERLOAD _CLC_DEF __CLC_GENTYPE
+__clc_rsqrt(__CLC_GENTYPE val) {
+  return __CLC_FP_LIT(1.0) / __clc_sqrt(val);
----------------
arsenm wrote:

```suggestion
__clc_rsqrt(__CLC_GENTYPE val) {
  #pragma clang fp contract(fast)
  return __CLC_FP_LIT(1.0) / __clc_sqrt(val);
```

https://github.com/llvm/llvm-project/pull/129045