build problem with CMAKE_OSX_ARCHITECTURES var

[CastagnaIT]

Hi on a Kodi software library we are using bento4 but our build system already set the CMAKE_OSX_ARCHITECTURES var

recently with commit https://github.com/axiomatic-systems/Bento4/commit/cbea428ae2f095afeb3c2b6ed25d692c9706de21 has been added this line https://github.com/axiomatic-systems/Bento4/blob/525027c6ef57bdd26636c9557239e7d559c612ad/CMakeLists.txt#L17 that set the CMAKE_OSX_ARCHITECTURES looks like that overwrite our config value, and cause to failed build of bento4

can you implement a logic to avoid to change/overwrite an existing CMAKE_OSX_ARCHITECTURES value?