Not just that...AMD's business does not line up with Dell's business at all.
Dell buys parts, repackages them, and sells them.
Dell wants to get into smartphones.
Buying AMD would do NOTHING for them. Before anyone says they can get CPUs cheaper, the cost of getting cheaper CPUs would be vastly increase risk, increase management, and rewriting business goals.
The only way I can see them going after this is if Dell thinks AMD has a lot of fat from fixed costs that can be trimmed out. Come in, cut fixed cost, turn high profit, collect big bonus.