Revert r319090, "COFF: Do not create SectionChunks for discarded comdat sections."
Revert r319090, "COFF: Do not create SectionChunks for discarded comdat sections."

Caused test failures in check-cfi on Windows.
http://lab.llvm.org:8011/builders/sanitizer-windows/builds/20284

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@319100 91177308-0d34-0410-b5e6-96231b3b80d8

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