cmd/compile: store combining not complete

[randall77]

https://go.dev/play/p/1mjcj4Qt_83

The PutUint64 should resolve to a single MOVQ. Instead it resolves to a MOVB/MOVL/MOVW/MOVB sequence.

Split off from #53324

@klauspost @wdvxdr1123

[agarciamontoro]

I'd like to work on this one, can I take it?

[gopherbot]

Change https://go.dev/cl/420115 mentions this issue: cmd/compile: store combining

[cuiweixie]

@randall77 I first work on rewrite rules. is the code right?