[Executorch] enable sleef consistently (#6705)

Pull Request resolved: https://github.com/pytorch/executorch/pull/6524

Earlier only android platofrms had support for sleef
ghstack-source-id: 252186435
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//oss lint broken on unrelated issue
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Differential Revision: [D64571782](https://our.internmc.facebook.com/intern/diff/D64571782/)

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