IR: Clean up some duplicated code in ConstantDataSequential creation. NFC

ConstantDataArray::getImpl and ConstantDataVector::getImpl had a lot
of copy pasta in how they handled sequences of constants. Break that
out into a couple of simple functions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254456 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed