Make EXTRACT_VECTOR_ELT a bit more flexible in terms of the returned

value.  Adjust other code to deal with that correctly.  Make 
DAGTypeLegalizer::PromoteIntRes_EXTRACT_VECTOR_ELT take advantage of 
this new flexibility to simplify the code and make it deal with unusual 
vectors (like <4 x i1>) correctly.  Fixes PR3037.

llvm-svn: 75176