Although i32 type is illegal in the backend, LA64 has pretty good
support for i32 types by using W instructions.
By adding n32 to the DataLayout string, middle end optimizations will
consider i32 to be a native type. One known effect of this is enabling
LoopStrengthReduce on loops with i32 induction variables. This can be
beneficial because C/C++ code often has loops with i32 induction
variables due to the use of `int` or `unsigned int`.
If this patch exposes performance issues, those are better addressed by
tuning LSR or other passes.
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