message: building outside the source tree was failing due to the build/tools directory not existing
diff: @@ -32,6 +32,7 @@ include_directories(${Z3_INCLUDE_DIRS})
  find_program(RE2C re2c)
  message(STATUS "RE2C: ${RE2C}")
  add_custom_command(OUTPUT "${CMAKE_BINARY_DIR}/tools/alive_lexer.cpp"
  + COMMAND ${CMAKE_COMMAND} -E make_directory "${CMAKE_BINARY_DIR}/tools"
  COMMAND ${RE2C} ARGS "-d" "-b" "--no-generation-date"
  "-o" "${CMAKE_BINARY_DIR}/tools/alive_lexer.cpp"
  "${PROJECT_SOURCE_DIR}/tools/alive_lexer.re"
  