[Ada] Static allocation of the TSD record

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

After this patch the compiler generates code that places the Type
Specific Data record associated with library level tagged types
in read-only memory.

2007-09-26  Javier Miranda  <miranda@adacore.com>
	    Eric Botcazou  <ebotcazou@adacore.com>

	* a-tags.adb: 
	(Get_HT_Link/Set_HT_Link): Updated to handle the additional level of
	 indirection added to the HT_Link component of the TSD. This is required
	 to statically allocate the TSD.

	* a-tags.ads: 
	Minor reordering of the declarations in the private part. Required to
	add a level of indirection to the contents of the TSD component HT_Link.
	This is required to statically allocate the TSD.

	* decl.c (gnat_to_gnu_entity) <object>: Do not exclude objects with
	Is_Statically_Allocated set from constant objects.
	Do not make exported constants created by the compiler volatile.
	(gnat_to_gnu_param): Do not treat an IN parameter whose address is taken
	as read-only.

	* trans.c (Identifier_to_gnu): For constants, unshare initializers
	before returning them.

	* exp_disp.ads, exp_disp.adb (Building_Static_DT): Spec moved to the
	public part of the package.
	(Make_DT): Move HT_Link component out of the TSD record. For this
	purpose Make_DT now declares a separate object that stores the
	HT_Link value, and initializes the TSD component with the address
	of this new object. The addition of this level of indirection is
	required to statically allocate the TSD because the TSD cannot
	have variable components.
	(Expand_Interface_Conversion): Improve the expanded code.
	(Expand_Interface_Thunk): Set Is_Thunk in the thunk entity.

	* sem_disp.adb (Check_Dispatching_Operation): In case of a body
	declaring a primitive operation ---allowed by RM 3.9.2 (13.e/2)---,
	if we are building static dispatch tables then we must not generate
	extra code to register the primitive because the dispatch table will
	be built at the end of the library package; otherwise we notify that
	we cannot build the static dispatch table.

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