Scheduler assumes SDDbgValue nodes are in source order. That's true currently. But add an assertion to verify it.
Scheduler assumes SDDbgValue nodes are in source order. That's true currently. But add an assertion to verify it.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@99501 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,chubbymaggie/asap,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,chubbymaggie/asap,apple/swift-llvm,dslab-epfl/asap,llvm-mirror/llvm,chubbymaggie/asap,llvm-mirror/llvm,apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,dslab-epfl/asap,llvm-mirror/llvm,llvm-mirror/llvm,chubbymaggie/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap