[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/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index dc830cb..fea5826 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -417,6 +417,10 @@
       return "DefiningSynthesizedFunction";
     case CodeSynthesisContext::Memoization:
       return "Memoization";
+    case CodeSynthesisContext::ConstraintsCheck:
+      return "ConstraintsCheck";
+    case CodeSynthesisContext::ConstraintSubstitution:
+      return "ConstraintSubstitution";
     }
     return "";
   }