Clear all the linetable state in clear(), fixing problems

with "clang t.i s.i" where the .i files contain line markers.
rdar://6667812


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@66619 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Basic/SourceManager.cpp

@@ -129,6 +129,7 @@ public:
   void clear() {
     FilenameIDs.clear();
     FilenamesByID.clear();
+    LineEntries.clear();
   }
   
   ~LineTableInfo() {}