ARROW-10873: [C++] Apple Silicon is reported as arm64 in CMake
ARROW-10873: [C++] Apple Silicon is reported as arm64 in CMake

I'll add a CI entry soon that cross-compiles using `conda`, for now I keep submitting patches when things break for me.

Closes #8893 from xhochy/ARROW-10873

Authored-by: Uwe L. Korn <5f6f0a63dee51498bdd8036770b3bad30ce7a5ac@quantco.com>
Signed-off-by: Krisztián Szűcs <6bab32dc957a05a87930e779f272342e159326fa@gmail.com>

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