[modules] Avoid the possibility of a redeclaration chain not being marked 'up
to date' after it gets updated.

llvm-svn: 230789
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 0ee2b2b..9d9885b 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -8317,10 +8317,9 @@
     PendingIncompleteDeclChains.clear();
 
     // Load pending declaration chains.
-    for (unsigned I = 0; I != PendingDeclChains.size(); ++I) {
+    for (unsigned I = 0; I != PendingDeclChains.size(); ++I)
       loadPendingDeclChain(PendingDeclChains[I]);
-      PendingDeclChainsKnown.erase(PendingDeclChains[I]);
-    }
+    PendingDeclChainsKnown.clear();
     PendingDeclChains.clear();
 
     // Make the most recent of the top-level declarations visible.