If preprocessed token introduced empty filename then use main translation unit's filename for debug info entries.

llvm-svn: 125672
diff --git a/clang/test/CodeGen/debug-info-crash.c b/clang/test/CodeGen/debug-info-crash.c
index e0c9dd4..8d6a360 100644
--- a/clang/test/CodeGen/debug-info-crash.c
+++ b/clang/test/CodeGen/debug-info-crash.c
@@ -19,3 +19,12 @@
     }
     );
 }
+
+// radar://9008853
+typedef struct P {
+  int x;
+} PS;
+# 1 ""
+void foo() {
+  PS p2;
+}