[clang] [Headers][X86] Add rounding and exception notes to conversions (PR #83447)

[Phoebe Wang via cfe-commits]

================
@@ -1405,11 +1413,12 @@ static __inline__ __m128d __DEFAULT_FN_ATTRS _mm_cvtss_sd(__m128d __a,
 
 /// Converts the two double-precision floating-point elements of a
 ///    128-bit vector of [2 x double] into two signed 32-bit integer values,
-///    returned in the lower 64 bits of a 128-bit vector of [4 x i32].
+///    returned in the lower 64 bits of a 128-bit vector of [4 x i32],
+///    truncating inexact results.
----------------
phoebewang wrote:

Oh, I took that simply as wrong infromation.

> Do you have a different suggestion for how to organize this information?

Not ideal, something like

```
/// Converts the two double-precision floating-point elements of a
///    128-bit vector of [2 x double] into two signed truncated
///    (rounded towards zero) 32-bit integer values,returned in the
///    most negative integer.
```

https://github.com/llvm/llvm-project/pull/83447