DebugInfo: Fix for CU index usage in 309507
DebugInfo: Fix for CU index usage in 309507

Not sure quite how I failed so clearly to test this, but anyway.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@309514 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit b83dd56dc1c68f400107ca51d29d6a2fe5922e2d)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm