Explain how to specify library location for MKL (#28779)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/24334.
I'm still kind of confused why `FindMKL.cmake` was unable to locate my MKL libraries. They are in the standard `/opt/intel/mkl` installation prefix on macOS. But at least with this more detailed error message, it will be easier for people to figure out how to fix the problem.
zhangguanheng66 xkszltl soumith
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28779
Differential Revision: D18170998
Pulled By: soumith
fbshipit-source-id: 47e61baadd84c758267dca566eb1fb8a081de92f
