[MAT-450] Add support for Windows 32-bit

To be considered in conjunction with PRs on OG-Lapack and OG-Maths.

Coverage is unchanged.

Details of changes:
- Addition of the BITS32 and BITS64 macros to determine the architecture in CMake.
- Only build dbg and std targets on 32-bit systems.
- Add the -ffloat-store flag on 32-bit Windows for consistency with 64-bit platforms.