ada: Improve attribute exclusion handling

Change the handling of some attribute mutual exclusions to use the
generic attribute exclusion lists, and fix some asymmetric exclusions by
adding the exclusions for always_inline after noinline or target_clones.

Aside from the new always_inline exclusions, the only change is
functionality is the choice of warning message displayed.  All warnings
about attribute mutual exclusions now use the same message.

gcc/ada/ChangeLog:

	* gcc-interface/utils.cc (attr_noinline_exclusions): New.
	(attr_always_inline_exclusions): Ditto.
	(attr_target_exclusions): Ditto.
	(attr_target_clones_exclusions): Ditto.
	(gnat_internal_attribute_table): Add new exclusion lists.
	(handle_noinline_attribute): Remove custom exclusion handling.
	(handle_target_attribute): Ditto.
	(handle_target_clones_attribute): Ditto.