[CMake] Fix standalone build for debugserver on macOS
[CMake] Fix standalone build for debugserver on macOS

Summary:
Quick-fix to avoid CMake config issue:
```
CMake Error at /path/to/lldb/cmake/modules/AddLLDB.cmake:116 (add_dependencies):
  Cannot add target-level dependencies to non-existent target "lldb-suite".
```

Reviewers: xiaobai, beanz

Subscribers: mgorny, lldb-commits

Differential Revision: https://reviews.llvm.org/D55032

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@347869 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb