When given a register and an immediate, it would generate imul imm,dst,dst however the 64-bit prefix was generated wrong and if dst was an extended register only the first operand would be an extended register. To fix this, change IMUL2 to not work on immediates anymore, and added a new IMUL3 that takes a destination register, source register, and immediate. Also, change compiler.cfg.two-operand to not two-operandize %mul-imm, since this isn't needed anymore.
This fixes the sporadic benchmark.tuple-arrays crash on 64-bit machines.
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