[Executorch][Portable] Compile portable ops with -O2 (#6588)

Pull Request resolved: https://github.com/pytorch/executorch/pull/6519

prefill toks: 21
decode: 11
after: e2e 621ms, prefil:: 370ms, decode: 43.84 tok/sec
ghstack-source-id: 251021625
@exported-using-ghexport

Differential Revision: [D64910578](https://our.internmc.facebook.com/intern/diff/D64910578/)

---------

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