This change enables specific compiler and linker options to be used in
the case that an arch/posix/os.arch.cmake file exists.
Note: os and arch in the above case are evaluations of
CMAKE_HOST_SYSTEM_NAME and CMAKE_HOST_SYSTEM_PROCESSOR.
Otherwise, the existing "generic" compiler and linker flags in
arch/posix/CMakeLists.txt are used.
Additional flags and checks are provided in
arch/posix/Linux.aarch64.cmake.
Added scripts/user_wordsize.py to detect if userspace is 64-bit or
32-bit, which should be consistent with the value of CONFIG_64BIT
for Aarch64 on Linux.
Fixes#24842
Signed-off-by: Christopher Friedt <chrisfriedt@gmail.com>