[AArch64] Use GISel for optnone functions (#174746) Currently, when SDAG is run on AArch64 and an `optnone` function is encountered, the selector is chosen as FastISel. AArch64 makes use of GlobalISel at O0 and this patch aims to align `optnone` with this functionality. A flag is exposed to enable this functionality for a given backend but, as AArch64 is currently the only backend I could find using GlobalISel at O0 this is the only one with it implemented. This flag is set when the target supports GlobalISel & GlobalISel hasn't been forced by the user, the target machine or by being at an optimisation level lower than `EnableGlobalISelAtO`. If this happens, the GlobalISel passes are included as shown in `llvm/test/CodeGen/AArch64/O3-pipeline.ll` and skipped by IRTranslator for functions not marked as `optnone`. In updating the tests based on this functionality, I found some unused check lines or run lines that mixed SDAG with GlobalISel pass names which have been fixed. --------- Co-authored-by: Matt Arsenault <arsenm2@gmail.com>
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