Track assumptions and restrictions separatly

  In order to speed up compile time and to avoid random timeouts we now
  separately track assumptions and restrictions. In this context
  assumptions describe parameter valuations we need and restrictions
  describe parameter valuations we do not allow. During AST generation
  we create a runtime check for both, whereas the one for the
  restrictions is negated before a conjunction is build.

  Except the In-Bounds assumptions we currently only track restrictions.

Differential Revision: http://reviews.llvm.org/D17247

llvm-svn: 262328