message: use OPT_SIZE macro in pybind11_add_module
diff: pybind11_add_module(
  enoki-python
  - THIN_LTO
  + THIN_LTO OPT_SIZE
  main.cpp
  implicit.cpp
  @@ -36,11 +36,4 @@ endif()
  set_target_properties(enoki-python PROPERTIES
  OUTPUT_NAME enoki_ext ${ENOKI_OUTPUT_DIRECTORY})
  -if (CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
  target_compile_options(enoki-python PRIVATE ${ENOKI_NATIVE_FLAGS})
  - if (NOT (${ENOKI_U_CMAKE_BUILD_TYPE} MATCHES "DEB"))
  - target_compile_options(enoki-python PRIVATE -g0 -Os)
  - endif()
  -elseif (MSVC)
  - target_compile_options(enoki-python PRIVATE /Os)
  -endif()
  