[Ada] Frontend cleanup: removal of attribute Is_Overriding_Operation

[Arnaud Charlet <charlet at adacore dot com>]

Abstract Syntax Tree entities have two fields associated with overriding
of type primitives: the flag Is_Overriding_Operation and the field
Overridden_Operation. This patch removes the flag Is_Overriding_Operation
and replaces all its occurrences by tests on the presence of attribute
Overridden_Operation.

Tested on x86_64-pc-linux-gnu, committed on trunk

2010-10-26  Javier Miranda  <miranda@adacore.com>

	* einfo.ads, einfo.adb (Is_Overriding_Operation): Removed.
	(Set_Is_Overriding_Operation): Removed.
	* sem_ch3.adb (Check_Abstract_Overriding): Remove redundant call to
	Is_Overriding_Operation.
	* exp_ch7.adb (Check_Visibly_Controlled): Remove redundant call to
	Is_Overriding_Operation.
	* sem_ch7.adb (Declare_Inherited_Private_Subprograms): Remove redundant
	call to Set_Is_Overriding_Operation.
	* sem_util.adb (Collect_Primitive_Operations): Replace test on
	Is_Overriding_Operation by test on the presence of attribute
	Overridden_Operation.
	(Original_Corresponding_Operation): Remove redundant call to attribute
	Is_Overriding_Operation.
	* sem_ch6.adb (Analyze_Abstract_Subprogram_Declaration): Remove
	redundant call to Is_Overriding_Operation.
	(Verify_Overriding_Indicator): Replace several occurrences of test on
	Is_Overriding_Operation by test on the presence of attribute
	Overridden_Operation.
	(Check_Convention): Replace test on Is_Overriding_Operation by test on
	the presence of Overridden_Operation.
	(Check_Overriding_Indicator): Add missing decoration of attribute
	Overridden_Operation. Minor code cleanup.
	(New_Overloaded_Entity): Replace occurrence of test on
	Is_Overriding_Operation by test on the presence of attribute
	Overridden_Operation. Remove redundant setting of attribute
	Is_Overriding_Operation plus minor code reorganization.
	Add missing decoration of attribute Overridden_Operation.
	* sem_elim.adb (Set_Eliminated): Replace test on
	Is_Overriding_Operation by test on the presence of Overridden_Operation.
	* sem_ch8.adb (Analyze_Subprogram_Renaming): Replace test on
	Is_Overriding_Operation by test on the presence of
	Overridden_Operation. Remove a redundant test on attribute
	Is_Overriding_Operation. 
	* lib-xref.adb (Generate_Reference): Replace test on
	Is_Overriding_Operation by test on the presence of Overridden_Operation.
	(Output_References): Replace test on Is_Overriding_Operation by test on
	the presence of Overridden_Operation.
	* sem_disp.adb (Override_Dispatching_Operation): Replace test on
	Is_Overriding_Operation by test on the presence of Overridden_Operation.
	Add missing decoration of attribute Overridden_Operation.

Attachment: difs
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