Fix crash when trying to generate debug info with program source from stdin

module.cpp

@@ -118,6 +118,16 @@ Module::Module(const char *fn) {
     // If we're generating debugging symbols, let the DIBuilder know that
     // we're starting a new compilation unit.
     if (diBuilder != NULL) {
+        if (filename == NULL) {
+            // Unfortunately we can't yet call Error() since the global 'm'
+            // variable hasn't been initialized yet.
+            fprintf(stderr, "Can't emit debugging information with no "
+                    "source file on disk.\n");
+            ++errorCount;
+            delete diBuilder;
+            diBuilder = NULL;
+        }
+        else {
             std::string directory, name;
             GetDirectoryAndFileName(g->currentDirectory, filename, &directory,
                                     &name);
@@ -129,6 +139,7 @@ Module::Module(const char *fn) {
                                          "-g", /* command line args */
                                          0 /* run time version */);
         }
+    }
 #endif // LLVM_2_8
 }