compel: abort PIE generation on undefined/external symbols

  As we meet this before, I think, we should abort generation here.
No point for making PIE with external symbols for us (at least, yet),
so let's break build than find the problem at runtime.

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

compel/handle-elf.c

@@ -319,7 +319,8 @@ int __handle_elf(void *mem, size_t size)
 					goto err;
 				}
 #else
-				continue;
+				pr_err("Unexpected undefined symbol: `%s'. External symbol in PIE?\n", name);
+				goto err;
 #endif
 			}