gnulib: update, and use the attribute module

* gnulib: Update.
* bootstrap.conf: Use attribute.
* src/system.h: Remove macros for attributes.
Adjust dependencies.
* src/scan-gram.l (DEPRECATED): Rename as...
(DEPRECATED_DIRECTIVE): this, to avoid the clash with the DEPRECATED macro.

lib/.gitignore

@@ -18,6 +18,7 @@
 /asnprintf.c
 /asprintf.c
 /assure.h
+/attribute.h
 /basename-lgpl.c
 /basename.c
 /binary-io.c