Fix mkldnn build on legacy x64 arch (#46082)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/45838
`ARCH_OPT_FLAGS` was the old name of `MKLDNN_ARCH_OPT_FLAGS`, which has been renamed in [this commit](https://github.com/oneapi-src/oneDNN/commit/2a011ff02ea2a4e2594c2f8450a1ca095eb22107#diff-a0abcbf647ed740b80615fb5b1614a44L97), but not updated in pytorch.
As its default value will be set to sse4.1, some kernels are going to fail on the legacy arch that does not support SSE4.1. This patch was to make this flag effective.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46082
Reviewed By: glaringlee
Differential Revision: D24252149
Pulled By: agolynski
fbshipit-source-id: 7079deed373d664763c5888feb28795e5235caa8
