Checking a build_vector for an all-ones value.

Checking a build_vector for an all-ones value.

Type legalization can zero-extend the elements of the build_vector node, so,
for example, we may have an <8 x i8> with i32 elements of value 255. That
should return 'true' for the vector being all ones.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153203 91177308-0d34-0410-b5e6-96231b3b80d8