message: Fix CMake binary dir discrepancy
  When used as a standalone project, both CMAKE_BINARY_DIR and
  PROJECT_BINARY_DIR yield the same value.
  However, when Alive2 added as a sub-project (via add_subdirectory),
  then CMAKE_BINARY_DIR and PROJECT_BINARY_DIR are different, which leads
  to a build failure.
  This patch fixes the discrepancy between two different values.
diff: @@ -49,23 +49,23 @@ endif()
  find_package(Git REQUIRED)
  add_custom_command(
  - OUTPUT "${CMAKE_BINARY_DIR}/version_gen.h.tmp"
  - COMMAND "${CMAKE_COMMAND}" -E echo_append "#define ALIVE_VERSION_MACRO " > "${CMAKE_BINARY_DIR}/version_gen.h.tmp"
  - COMMAND "${GIT_EXECUTABLE}" describe --tags --dirty --always >> "${CMAKE_BINARY_DIR}/version_gen.h.tmp"
  + OUTPUT "${PROJECT_BINARY_DIR}/version_gen.h.tmp"
  + COMMAND "${CMAKE_COMMAND}" -E echo_append "#define ALIVE_VERSION_MACRO " > "${PROJECT_BINARY_DIR}/version_gen.h.tmp"
  + COMMAND "${GIT_EXECUTABLE}" describe --tags --dirty --always >> "${PROJECT_BINARY_DIR}/version_gen.h.tmp"
  WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
  VERBATIM
  )
  add_custom_command(
  - DEPENDS "${CMAKE_BINARY_DIR}/version_gen.h.tmp"
  - OUTPUT "${CMAKE_BINARY_DIR}/version_gen.h"
  - COMMAND "${CMAKE_COMMAND}" -E copy_if_different "${CMAKE_BINARY_DIR}/version_gen.h.tmp" "${CMAKE_BINARY_DIR}/version_gen.h"
  - COMMAND "${CMAKE_COMMAND}" -E remove -f "${CMAKE_BINARY_DIR}/version_gen.h.tmp"
  + DEPENDS "${PROJECT_BINARY_DIR}/version_gen.h.tmp"
  + OUTPUT "${PROJECT_BINARY_DIR}/version_gen.h"
  + COMMAND "${CMAKE_COMMAND}" -E copy_if_different "${PROJECT_BINARY_DIR}/version_gen.h.tmp" "${PROJECT_BINARY_DIR}/version_gen.h"
  + COMMAND "${CMAKE_COMMAND}" -E remove -f "${PROJECT_BINARY_DIR}/version_gen.h.tmp"
  WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
  VERBATIM
  )
  add_custom_target(
  generate_version ALL
  - DEPENDS "${CMAKE_BINARY_DIR}/version_gen.h"
  + DEPENDS "${PROJECT_BINARY_DIR}/version_gen.h"
  WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}"
  )
  @@ -79,10 +79,10 @@ if (RE2C)
  else()
  message(SEND_ERROR "re2c executable not found")
  endif()
  -add_custom_command(OUTPUT "${CMAKE_BINARY_DIR}/tools/alive_lexer.cpp"
  - COMMAND ${CMAKE_COMMAND} -E make_directory "${CMAKE_BINARY_DIR}/tools"
  +add_custom_command(OUTPUT "${PROJECT_BINARY_DIR}/tools/alive_lexer.cpp"
  + COMMAND ${CMAKE_COMMAND} -E make_directory "${PROJECT_BINARY_DIR}/tools"
  COMMAND ${RE2C} ARGS "-d" "-b" "-T" "--no-generation-date"
  - "-o" "${CMAKE_BINARY_DIR}/tools/alive_lexer.cpp"
  + "-o" "${PROJECT_BINARY_DIR}/tools/alive_lexer.cpp"
  "${PROJECT_SOURCE_DIR}/tools/alive_lexer.re"
  DEPENDS "tools/alive_lexer.re")
  @@ -123,7 +123,7 @@ set(TOOLS_SRCS
  add_library(tools STATIC ${TOOLS_SRCS})
  set(UTIL_SRCS
  - "${CMAKE_BINARY_DIR}/version_gen.h"
  + "${PROJECT_BINARY_DIR}/version_gen.h"
  util/version.cpp
  util/compiler.cpp
  util/config.cpp
  @@ -211,7 +211,7 @@ endif()
  add_executable(alive
  "tools/alive.cpp"
  - "${CMAKE_BINARY_DIR}/tools/alive_lexer.cpp"
  + "${PROJECT_BINARY_DIR}/tools/alive_lexer.cpp"
  "tools/alive_parser.cpp"
  )
  target_link_libraries(alive PRIVATE ${ALIVE_LIBS})
  