Try to appease MSVC after r265456
Try to appease MSVC after r265456

I can't remember if adding `= default` will make MSVC happy, or if I
have to spell this out.  Let's try the cleaner version first.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@265465 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 3444a406d31d47784afc8ae96c0f2be32e23bd18)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm