Update CMakeLists.txt

[vaparetia]

Added 32bit compile options for building 32bit binaries by default on Linux

[JayFoxRox]

This should be handled through a CMake Toolchain file. Setting default to 32-bit wouldn't even work on my system because it's purely 64-bit, so compilation would fail.

Default should be to do a native build, if people want something else, they can use a toolchain file to compile for whatever system they want.

I suggest that this should be closed. But I'll let other maintainers decide.