This is my typical build-script invocation. Using this lldb --repl works for me.
swift/utils/build-script -r --lldb -- --skip-build-benchmarks --skip-test-cmark --skip-test-swift --lldb-use-system-debugserver --lldb-test-swift-only --lldb-build-with-cmake --llvm-enable-modules=true
Does this configuration work for you?