[Ada] Compiler crash on -gnata -O2

[Ada] Compiler crash on -gnata -O2

gcc/ada/

	* contracts.adb (Build_Unique_Name): New subprogram.
	(Make_Class_Precondition_Subps): Use Build_Unique_Name to
	generate the names of the call helpers and the name of indirect
	call wrappers.
	* freeze.adb (Needs_Wrapper): Remove dead code.
	(Check_Inherited_Conditions): Defer building helpers and ICW
	until all the dispatch table wrappers have been built and
	analyzed. Required to ensure uniqueness in their names because
	when building these wrappers for overlapped subprograms their
	homonym number is not definite until they have been analyzed.