[Executorch] Make apple take accelerate path for blas (#6603)

Pull Request resolved: https://github.com/pytorch/executorch/pull/6523

For some reason fbobjc_exported_preprocessor_flags does not seems to work. Thus
taking 'select' route which seems to work.
ghstack-source-id: 251185499
@exported-using-ghexport

//oss lint broken on unrelated issue
@bypass-github-export-checks
@exported-using-ghexport

Differential Revision: [D64499608](https://our.internmc.facebook.com/intern/diff/D64499608/)

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Co-authored-by: Kimish Patel <kimishpatel@fb.com>