use simd_reduce_add_ordered on aarch64

[usamoi]

This makes some intrinsics to work in Miri.

The idea is from #1925:

modifies the integer reduce_add and reduce_mul intrinsics to use simd_reduce_add_ordered and simd_ordered_mul_ordered, respectively. As integer algebra is associative, it doesn't matter for correctness, and LLVM will use the most performant arrangement. The reason is that rustc_const_eval only implements these ordered reduction intrinsics, unordered reduction seems to be tricky to implement in const_eval

[rustbot]

r? @Amanieu

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