[Concepts] Concept Specialization Expressions

Part of C++20 Concepts implementation effort. Added Concept Specialization Expressions that are created when a concept is refe$

D41217 on Phabricator.

(recommit after fixing failing Parser test on windows)

llvm-svn: 374903
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index 0f3a272..76fd10d 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -1314,6 +1314,7 @@
   case Expr::SizeOfPackExprClass:
   case Expr::StringLiteralClass:
   case Expr::SourceLocExprClass:
+  case Expr::ConceptSpecializationExprClass:
     // These expressions can never throw.
     return CT_Cannot;