[Frontend] Disable value name discarding for all sanitizers.
[Frontend] Disable value name discarding for all sanitizers.

ASan also relies on names on allocas and will emit unhelpful output if
they're not present. Just force-enable value names for now. Should
unbreak release builds of asan.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@263429 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang