Add test coverage for invalid conversion functions with default args.
Add test coverage for invalid conversion functions with default args.

This currently leaks memory (PR19689) but wasn't covered by tests, so LSan
couldn't find it.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@208477 91177308-0d34-0410-b5e6-96231b3b80d8

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