Change Preprocessor::EnterSourceFile to make ErrorStr non-optional, clients should be forced to deal with error conditions.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@90700 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/PPLexerChange.cpp b/lib/Lex/PPLexerChange.cpp
index 1580b87..5cdfeaf 100644
--- a/lib/Lex/PPLexerChange.cpp
+++ b/lib/Lex/PPLexerChange.cpp
@@ -65,7 +65,7 @@
 /// EnterSourceFile - Add a source file to the top of the include stack and
 /// start lexing tokens from it instead of the current buffer.
 bool Preprocessor::EnterSourceFile(FileID FID, const DirectoryLookup *CurDir,
-                                   std::string *ErrorStr) {
+                                   std::string &ErrorStr) {
   assert(CurTokenLexer == 0 && "Cannot #include a file inside a macro!");
   ++NumEnteredSourceFiles;
 
@@ -81,8 +81,8 @@
   
   // Get the MemoryBuffer for this FID, if it fails, we fail.
   const llvm::MemoryBuffer *InputFile =
-    getSourceManager().getBuffer(FID, ErrorStr);
   if (InputFile == 0)
+    getSourceManager().getBuffer(FID, &ErrorStr);
     return true;
   
   EnterSourceFileWithLexer(new Lexer(FID, InputFile, *this), CurDir);