message: [CMake] Don't clobber linker flags already set
diff: # Set the correct rpath to locate libswiftCore.
  if (LLDB_BUILD_FRAMEWORK)
  - set(CMAKE_EXE_LINKER_FLAGS "-Wl,-rpath \
  + set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-rpath \
  -Wl,${CMAKE_BINARY_DIR}/${LLDB_FRAMEWORK_INSTALL_DIR}/${LLDB_FRAMEWORK_RESOURCE_DIR}/Swift/macosx")
  elseif( CMAKE_SYSTEM_NAME MATCHES "Linux" )
  # Set the correct rpath to locate libswiftCore
  - set(CMAKE_EXE_LINKER_FLAGS "-Wl,-rpath,${CMAKE_BINARY_DIR}/../swift-linux-x86_64/lib${LLVM_LIBDIR_SUFFIX}/swift/linux -Wl,-ldl")
  + set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} \
  + -Wl,-rpath,${CMAKE_BINARY_DIR}/../swift-linux-x86_64/lib${LLVM_LIBDIR_SUFFIX}/swift/linux -Wl,-ldl")
  set(CMAKE_INSTALL_RPATH "$ORIGIN/../lib/swift/linux:${CMAKE_INSTALL_RPATH}")
  endif()
  