Add blas compare example (#47058)
Summary:
Adds a standalone script which can be used to test different BLAS libraries. Right now I've deliberately kept it limited (only a couple BLAS libs and only GEMM and GEMV). It's easy enough to expand later.
CC ngimel
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47058
Reviewed By: zhangguanheng66
Differential Revision: D25078946
Pulled By: robieta
fbshipit-source-id: b5f7f7ec289d59c16c5370b7a6636c10a496b3ac
