Suppress "control reaches end of non-void function" warning when compiling with gcc.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185439 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaLambda.cpp b/lib/Sema/SemaLambda.cpp
index bc99d58..b2dbf05 100644
--- a/lib/Sema/SemaLambda.cpp
+++ b/lib/Sema/SemaLambda.cpp
@@ -116,6 +116,8 @@
     //  -- default arguments appearing in class definitions
     return &ExprEvalContexts.back().getMangleNumberingContext();
   }
+
+  llvm_unreachable("unexpected context");
 }
 
 CXXMethodDecl *Sema::startLambdaDefinition(CXXRecordDecl *Class,