Fix compiler error in swapBytes64 for rare architectures (#16418)
Summary:
swapBytes64 used to use SwapByteOrder_32 and value, both of which dont exist. This commit rewrites that part from scratch.
This happened on Debugbuild on Microsoft compiler. For that case " && !defined(_DEBUG)" is also removed, because _byteswap_uint64 works fine in debug mode (if it is necessary it should me commented why).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16418
Differential Revision: D13843306
Pulled By: ezyang
fbshipit-source-id: dde1c7baeccec3aaa750d4b7200b3f4ccb4a00cb
