Entering the main source file in the preprocessor can fail if the
source file has been changed. Handle that failure more gracefully.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@98727 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/PrintPreprocessedOutput.cpp b/lib/Frontend/PrintPreprocessedOutput.cpp
index 44e0e13..02afd24 100644
--- a/lib/Frontend/PrintPreprocessedOutput.cpp
+++ b/lib/Frontend/PrintPreprocessedOutput.cpp
@@ -448,7 +448,8 @@
 static void DoPrintMacros(Preprocessor &PP, llvm::raw_ostream *OS) {
   // -dM mode just scans and ignores all tokens in the files, then dumps out
   // the macro table at the end.
-  PP.EnterMainSourceFile();
+  if (PP.EnterMainSourceFile())
+    return;
 
   Token Tok;
   do PP.Lex(Tok);
@@ -495,7 +496,8 @@
   PP.addPPCallbacks(Callbacks);
 
   // After we have configured the preprocessor, enter the main file.
-  PP.EnterMainSourceFile();
+  if (PP.EnterMainSourceFile())
+    return;
 
   // Consume all of the tokens that come from the predefines buffer.  Those
   // should not be emitted into the output and are guaranteed to be at the