* Makefile.in (cppexp.o): Depend on cpphash.h.
	* cppexp.c (cpp_lex): Handle `defined (xxx)' for poisoned xxx.
	Include cpphash.h.
	* cpphash.c (special_symbol): Handle plain `xxx' for poisoned xxx.
	* cpplib.c (do_define): Generalise to handle poisoned definitions,
	redefining poisoned identifiers, etc.
	(do_undef): Don't allow poisoned identifiers to be undefined.
	(do_pragma): Add #pragma poison.
	(do_xifdef): Handle `#ifdef xxx' for poisoned xxx.

	* cccp.c: Add T_POISON node type.
	(special_symbol): Handle `defined(xxx)' and plain `xxx' for
	poisoned xxx.
	(do_define): Generalise to handle poisoned definitions,
	redefining poisoned identifiers, etc.
	(do_undef): Don't allow poisoned identifiers to be undefined.
	(do_pragma): Add #pragma poison.
	(do_xifdef): Handle `#ifdef xxx' for poisoned xxx.

	* c-pragma.c (handle_pragma_token): Ignore #pragma poison.
	* c-pragma.h: Add ps_poison state.  We now always have generic
	pragmas.

From-SVN: r29224