[DAGCombiner] Merge together duplicate checks for folding fold (select C, 1,...

[DAGCombiner] Merge together duplicate checks for folding fold (select C, 1, X) -> (or C, X)  and  folding (select C, X, 0) -> (and C, X). Also be consistent about checking that both the condition and the result type are i1. NFC

I guess previously we just assumed if the result type was i1, then the condition type must also be i1?

llvm-svn: 291548