Revert "Remove dead option." Some tests in debuginfo-tests require the system-darwin feature.
Revert "Remove dead option."
Some tests in debuginfo-tests require the system-darwin feature.

This reverts commit 179670.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@201800 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang