When enabling LLDB tests with LLVM_ENABLE_RUNTIMES=libcxx CMake will fail with:
LLDB test suite requires libc++, but it is currently disabled.
The issue is that the targets in LLVM_ENABLE_RUNTIMES are configured after the targets in LLVM_ENABLE_PROJECTS, so at this point the check for the cxx target will fail. CMake will add a dependency for a target that does not exist yet however, so by first checking for libcxx in LLVM_ENABLE_RUNTIMES we ensure that the cxx target will be present at build time.
% cmake -G Ninja -C ~/local/llvm-project/lldb/cmake/caches/Apple-lldb-macOS.cmake -DLLVM_ENABLE_PROJECTS="clang;lldb" -DLLVM_ENABLE_RUNTIMES="libcxx" -DLIBCXX_INCLUDE_TESTS=NO ~/local/llvm-project/llvm % ninja check-lldb