Fix IS_SPMM_AVAILABLE macro definition (#42643)
Summary:
This should fix CUDA-11 on Windows build issue
`defined` is not a function, and so it can not be used in macro substitution.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42643
Reviewed By: pbelevich, xw285cornell
Differential Revision: D22963420
Pulled By: malfet
fbshipit-source-id: cccf7db0d03cd62b655beeb154db9e628aa749f0
