message: [lldb-dotest] Check that swif compiler and libs path exists.
  The variable is not known at configuration
  time so we need to read LLDB_SWIFTC and LLDB_SWIFT_LIBS which are (will
  be) set by the build script.
diff: @@ -5,10 +5,8 @@ import sys
  dotest_path = '@LLDB_SOURCE_DIR@/test/dotest.py'
  dotest_args_str = '@LLDB_DOTEST_ARGS@'
  -
  -swift_build_dir = '@LLDB_PATH_TO_SWIFT_BUILD'
  -swift_compiler = os.path.join(swift_build_dir, 'bin', 'swiftc')
  -swift_library = os.path.join(swift_build_dir, 'lib', 'swift')
  +swift_compiler = '@LLDB_SWIFTC'
  +swift_library = '@LLDB_SWIFT_LIBS'
  if __name__ == '__main__':
  wrapper_args = sys.argv[1:]
  @@ -16,7 +14,9 @@ if __name__ == '__main__':
  # Build dotest.py command.
  cmd = [dotest_path, '-q']
  cmd.extend(dotest_args)
  + if os.path.exists(swift_compiler):
  cmd.extend(['--swift-compiler', swift_compiler])
  + if os.path.exists(swift_library):
  cmd.extend(['--swift-library', swift_library])
  cmd.extend(wrapper_args)
  # Invoke dotest.py
  