[clang-doc] Sort index elements case insensitive

Implement logic to compare the references of the index case insensitive.

Differential revision: https://reviews.llvm.org/D66299

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@369068 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed