ConstantFolding: Don't crash when encountering vector GEP

ConstantFolding tried to cast one of the scalar indices to a vector
type. Instead, use the vector type only for the first index (which
is the only one allowed to be a vector) and use its scalar type
otherwise.

Fixes PR31250.

Reviewers: majnemer
Differential Revision: https://reviews.llvm.org/D27389

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289073 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed