CMAKE_SYSTEM_PROCESSORΒΆ
When not cross-compiling, this variable has the same value as the
CMAKE_HOST_SYSTEM_PROCESSOR variable. In many cases,
this will correspond to the target architecture for the build, but
this is not guaranteed. (E.g. on Windows, the host may be AMD64
even when using a MSVC cl compiler with a 32-bit target.)
When cross-compiling, a CMAKE_TOOLCHAIN_FILE should set
the CMAKE_SYSTEM_PROCESSOR variable to match target architecture
that it specifies (via CMAKE_<LANG>_COMPILER and perhaps
CMAKE_<LANG>_COMPILER_TARGET).