Also avoid warning on -flto/-fno-lto on linux.
Also avoid warning on -flto/-fno-lto on linux.

On OS X a .s file is preprocessed, it is not on linux, which is why the warning was still
showing up on linux but not OS X.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@225095 91177308-0d34-0410-b5e6-96231b3b80d8

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