Fix `codegen_atomic_binop` for `atomic_ptr` #6180

Job	Run time
benchcomp-tests	4m 14s
perf	38m 40s
bookrunner	16m 42s
regression (macos-13)	28m 22s
write-json-symtab-regression	12m 6s
regression (ubuntu-20.04)	20m 31s
regression (ubuntu-22.04)	21m 27s
	2h 22m 2s

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