ArrayRef'ize Sema::FinalizeDeclaratorGroup, Sema::BuildDeclaratorGroup and
Sema::ActOnDocumentableDecls.

Patch by Robert Wilhelm.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185931 91177308-0d34-0410-b5e6-96231b3b80d8