Copy file and line info during a macro expansion.

The file and line number information needs to be copied when
doing a macro expansion. This prevents a macro that expands to
an `ifdef of other construct that needs to push the stack
from core dumping.

ivlpp/lexor.lex

@@ -1362,6 +1362,8 @@ static void do_expand(int use_args)
         }
 
         isp->next = istack;
+        isp->path = strdup(istack->path);
+        isp->lineno = istack->lineno;
         istack->yybs = YY_CURRENT_BUFFER;
         istack = isp;