35a3e31#diff-1e7de1ae2d059d21e1dd75d5812d5a34b0222cef273b7c3a2af62eb747f9d20aR440-R441

set(ASIOEXEC_ASIO_CONFIG_FILE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/include/asioexec)
configure_file(include/asioexec/asio_config.hpp.in ${ASIOEXEC_ASIO_CONFIG_FILE_PATH}/asio_config.hpp)

I think setting the output to ${CMAKE_CURRENT_BINARY_DIR}/stdexec_generated/include/asioexec and then added via target_include_directories(stdexec PUBLIC ${CMAKE_CURRENT_BINARY_DIR}/stdexec_generated/include) is the better way here.