[clang] [Clang] Add __builtin_(elementwise|reduce)_(max|min)imum (PR #110198)

[Matt Arsenault via cfe-commits]

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@@ -706,6 +706,12 @@ Unless specified otherwise operation(±0) = ±0 and operation(±infinity) = ±in
                                              representable values for the signed/unsigned integer type.
  T __builtin_elementwise_sub_sat(T x, T y)   return the difference of x and y, clamped to the range of        integer types
                                              representable values for the signed/unsigned integer type.
+ T __builtin_elementwise_maximum(T x, T y)   return x or y, whichever is larger. If exactly one argument is   integer and floating point types
+                                             a NaN, return the other argument. If both arguments are NaNs,
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arsenm wrote:

This doesn't fully explain the semantics, and I'd like to avoid trying to re-explain all the details in every instance of this. Can you just point this to some other description of the semantics? 

https://github.com/llvm/llvm-project/pull/110198