Disallow 32-bit Windows builds.

Can be forced by setting OGS_32_BIT=ON

scripts/cmake/ProjectSetup.cmake

+# Check requirements / supported configurations
+if(MSVC AND NOT HAVE_64_BIT AND NOT OGS_32_BIT)
+    message(FATAL_ERROR "Building OGS on Windows with 32-bit is not supported! \
+Either use the correct generator, e.g. 'Visual Studio 14 2015 Win64' or define \
+'-DOGS_32_BIT=ON' if you know what you are doing.")
+endif()
+
 # Set build directories
 set(EXECUTABLE_OUTPUT_PATH ${PROJECT_BINARY_DIR}/bin)
 set(LIBRARY_OUTPUT_PATH ${PROJECT_BINARY_DIR}/lib)