Report syntax errors in natives when building with mksnapshot.

src/isolate.cc

Index: src/isolate.cc
===================================================================
--- src/isolate.cc	(revision 11679)
+++ src/isolate.cc	(working copy)
@@ -1131,8 +1131,18 @@
       // to the console for easier debugging.
       int line_number = GetScriptLineNumberSafe(location->script(),
                                                 location->start_pos());
-      OS::PrintError("Extension or internal compilation error at line %d.\n",
-                     line_number);
+      if (exception->IsString()) {
+        OS::PrintError(
+            "Extension or internal compilation error: %s in %s at line %d.\n",
+            *String::cast(exception)->ToCString(),
+            *String::cast(location->script()->name())->ToCString(),
+            line_number);
+      } else {
+        OS::PrintError(
+            "Extension or internal compilation error in %s at line %d.\n",
+            *String::cast(location->script()->name())->ToCString(),
+            line_number);
+      }
     }
   }