/nostdlib[+ | -]
The /nostdlib option prevents the import of mscorlib.dll, which defines the entire System namespace. Use this option if you want to define or create your own System namespace and objects.
If you do not specify /nostdlib, mscorlib.dll will be imported into your program (same as specifying /nostdlib-). If you specify /nostdlib, it is the same as specifying /nostdlib+.