[Order Files] Don't use empty order files
[Order Files] Don't use empty order files

LD64 does optimization on symbol layouts that gets disabled whenever an order file is passed (even if it is empty). This change prevents disabling that optimization, and still enables iterative generation and usage of order files.

If the order file is empty it does not setup the order file flags, instead it sets the empty order file as a configuration dependency. When the order file changes it will then trigger a re-configuration that adds the linker flag.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@278306 91177308-0d34-0410-b5e6-96231b3b80d8

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