ada: Improve warning on abstract equality

ada: Improve warning on abstract equality

In many cases, we warn if an abstract equality function
is called implicitly. In the case of record equality,
this patch adds a mention of the particular component_declaration
for which an abstract "=" is invoked; otherwise it is hard to
understand the warning for record types with many components.

gcc/ada/ChangeLog:

	* exp_ch4.adb (Warn_On_Abstract_Equality_For_Component):
	Add additional information in the record-component case.