* system.h (TARGET_ESC): Move to ...
	* defaults.h (TARGET_ESC): ... here.
	* target-def.h (TARGET_VALID_DECL_ATTRIBUTE,
	TARGET_VALID_TYPE_ATTRIBUTE): Default to a no-op handler.
	* tree.c (default_valid_attribute_p): New.
	(valid_machine_attribute): Handlers can not be NULL.
	* tree.h (default_valid_attribute_p): New.
	* doc/tm.texi: Document TARGET_ESC.
	* cp/decl2.c (import_export_class): Update.

From-SVN: r43615