Add support for unified_shared_memory clause on requires directive

llvm-svn: 343472
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 570a1e1..08cfa6b 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -6932,3 +6932,6 @@
 }
 
 void OMPClauseWriter::VisitOMPUnifiedAddressClause(OMPUnifiedAddressClause *) {}
+
+void OMPClauseWriter::VisitOMPUnifiedSharedMemoryClause(
+    OMPUnifiedSharedMemoryClause *) {}