Hopefully fix the windows build.
Support disabling of the security subsystem (CAS/CoreCLR).

This could still use some future work. For example, we could get
rid of lots of security code in the class libs. There are also some
functions in the runtime that don't get removed because we don't
use the stub macro approach for all public security functions.

Based on Sebastien's patch.
Try to recover expressions aftern named argument
Remove System.Net.Http from MT mobile build