cmake platform autodetect

[tansy]

There is somewhat confusing construction of configuration in CMakeLists.txt that will automatically run 64-bit configuration on 32-bit system.

Initial BUILD_X64=ON
Initial CMAKE_BUILD_TYPE=
rdopng build type: Release
Building 64-bit
-- Configuring done

Even if someone makes that effort co cross compile to x64 on x86 they will not run it anyway. Opposite situation - cross compiling and running 32-bit program on 64-bit system - is absolutely possible. It would be better to set 32-bit build false by default and auto detect platform.

# on 32-bit system
Initial BUILD_X32=OFF
(...)
Building 32-bit

# on 64-bit system
Initial BUILD_X32=OFF
(...)
Building 64-bit

If one wanted to force 32-bit compilation they can do that with $ cmake -DBUILD_X32 ..

# on 64-bit system
Initial BUILD_X32=TRUE
(...)
Building 32-bit

[richgel999]

Thanks! I suck at cmake. Will test this and integrate the next time I spend a few days working on this project.