In this PR we account for possible <1 x LLVM Type> input to ensure that
we produce legal vector types during type inference.
We modify an LLVM type to conform with future transformations in
IRTranslator, if it's a <1 x Type> vector type, replacing it by the
element type, because <1 x Type> vector type is not a legal vector type
in LLT and IRTranslator will represent it as the scalar eventually.