Add a HasSuppressionType method into SuppressionContext

Extending SuppressionContext to add a HasSuppressionType method that tells whether a certain suppression type is currently used or not. It's a step to implement issue suppressions for ASan, see http://reviews.llvm.org/D6280.

Reviewed at http://reviews.llvm.org/D6443



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@222954 91177308-0d34-0410-b5e6-96231b3b80d8