The Lexer constructor expects a source location at the start of the
file buffer, not at the start of lexing.

Fixes assertion hit in format diagnostics. rdar://11418366

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156647 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index afc7410..ba2cc8e 100644
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -708,8 +708,8 @@
     LangOpts.Trigraphs = true;
     
     // Create a lexer starting at the beginning of this token.
-    Lexer TheLexer(StrTokSpellingLoc, Features, Buffer.begin(), StrData,
-                   Buffer.end());
+    Lexer TheLexer(SM.getLocForStartOfFile(LocInfo.first), Features,
+                   Buffer.begin(), StrData, Buffer.end());
     Token TheTok;
     TheLexer.LexFromRawLexer(TheTok);