None also a valid CMake BUILD_TYPE

[CoelacanthusHex]

This BUILD_TYPE is normally used in distro packaging so the packager can ensure libtsm was built with their compile options. It's also the default value of CMAKE_BUILD_TYPE.

See also https://wiki.archlinux.org/title/CMake_package_guidelines#CMake_can_automatically_override_the_default_compiler_optimization_flag