[clang-doc] Generate an HTML index file

clang-doc now generates a file that contains only an index to all the
infos that can be used as the landing page for the generated website.

Differential Revision: https://reviews.llvm.org/D65918

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@368484 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed