[Ada] Store the value of 'alignment of tagged types in the TSD

[Arnaud Charlet <charlet at adacore dot com>]

This patch removes primitive 'alignment to tagged types. This value
is now stored in the Type Specific Data record associated with each
tagged type since it is information known at compile-time.

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

2011-12-12  Javier Miranda  <miranda@adacore.com>

	* a-tags.ads (Alignment): New TSD field.
	(Max_Predef_Prims): Value lowered to 15 (or 9 in case of
	configurable runtime) Update documentation of predefined
	primitives since Alignment has been removed.
	* exp_disp.ads Update documentation of slots of dispatching
	primitives.
	* exp_disp.adb (Default_Prim_Op_Position): Update slot
	values since alignment is no longer a predefined primitive.
	(Is_Predefined_Dispatch_Operation): Remove _alignment.
	(Is_Predefined_Internal_Operation): Remove _alignment.
	(Make_DT): Update static test on the value stored in a-tags.ads
	for Max_Predef_Prims; store the value of 'alignment in the TSD.
	* exp_atag.ads, exp_atag.adb (Build_Get_Alignment): New subprogram
	that retrieves the alignment from the TSD
	* exp_util.adb (Build_Allocated_Deallocate_Proc): For deallocation
	of class-wide types obtain the value of alignment from the TSD.
	* exp_attr.adb (Expand_N_Attribute_Reference): For 'alignment
	applied to a class-wide type invoke Build_Get_Alignment to
	generate code which retrieves the value of the alignment from
	the TSD.
	* rtsfind.ads (RE_Alignment): New Ada.Tags entity
	* sem_ch13.adb (Analyze_Attribute_Definition_Clause): For tagged
	types if the value of the alignment is bigger than the Maximum
	alignment then set the value of the alignment to the Maximum
	alignment and report a warning.
	* exp_ch3.adb (Make_Predefined_Primitive_Specs): Do not generate
	spec of _alignment.
	(Predefined_Primitive_Bodies): Do not generate body of _alignment.

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