Debug.cpp: Use DIBuilder::insertDeclare(), corresponding to LLVM r218787.

FIXME: Do we need DebugInfo::InsertDeclare() yet?

git-svn-id: https://llvm.org/svn/llvm-project/dragonegg/trunk@219613 91177308-0d34-0410-b5e6-96231b3b80d8