Install: add arm_neon.h header back
Install: add arm_neon.h header back

I'd gone too far pruning aarch64_simd.h this time and took out one
instance of arm_neon.h. This should restore us to the status quo.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@205111 91177308-0d34-0410-b5e6-96231b3b80d8

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,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,llvm-mirror/clang