[ThinLTO] Make ValueInfo operator!= consistent with operator== (NFC)
[ThinLTO] Make ValueInfo operator!= consistent with operator== (NFC)

Compare Ref pointers instead of GUID, to handle comparison with special
empty/tombstone ValueInfo. This was already done for operator==, to
support inserting ValueInfo into DenseMap, but I need the operator!=
side change for upcoming AsmParser summary parsing support.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@334111 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm