This fixes ! to work as documented in a memory region attribute list.

This fixes ! to work as documented in a memory region attribute list.
	From Thomas Zenker <thz@lennartz-electronic.de>:
	* ldgram.y (attributes_opt): Use attributes_list instead of NAME.
	(attributes_list, attributes_string): New nonterminals.
	* ldlang.c (lang_set_flags): Add invert parameter.  Don't handle
	'!'.
	* ldlang.c (lang_set_flags): Update declaration.