Refactor native/cpu/zmath.h (#38037)
Summary:
There is now a `zmath.h` and `zmath_std.h`, where the latter is the copy-paste of the original `zmath.h` and supporting `std::complex`, and `zmath.h` is for supporting `c10::complex`. `zmath_std.h` will be removed eventually.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38037
Differential Revision: D21518177
Pulled By: anjali411
fbshipit-source-id: 18552e955dc31f95870f34962d709de0444804f6
