[clang] Add _MM_FROUND_TO_NEAREST_TIES_EVEN to avx512fintrin.h (PR #99691)

[Robin Charles Gilbert via cfe-commits]

robincharlesgilbert wrote:

Former dev for the math libraries of the Intel compiler here.

It is true that the name _MM_FROUND_TO_NEAREST_INT is quite old. For instance (since I see an Intel document quoted here for which I may or may not have been one of the authors, and that "all common compilers" is typical codeword for MSVC or GCC), this name has been sleeping in GCC inside config/i386/smmintrin.h for 17 years now --- a file, like many before and since, that was added by an Intel colleague, H.J. Lu, in GCC. However, even back then, this was seen as a problematic name in the microscopic world of computational arithmetic (which is called Numerics at Intel), since, indeed, it does **not** round to an integer. Given that's the default rounding mode, that name did not leave the greatest impression. At least it's _MM_ROUND_NEAREST in xmmintrin.h, but that was a few years earlier.

This commit does not change the existing name, it only adds a much less confusing one while respecting the nomenclature pattern. It will give the name that should have been, and it will help remove some confusion about what round to nearest actually is.

https://github.com/llvm/llvm-project/pull/99691