decl.c (gnat_to_gnu_entity): Create a mere scalar constant instead of a reference for renaming of scalar literal.

	* gcc-interface/decl.c (gnat_to_gnu_entity) <object>: Create a mere
	scalar constant instead of a reference for renaming of scalar literal.
	Do not create a new object for constant renaming except for a function
	call.  Make sure a VAR_DECL is created for the renaming pointer.
	* gcc-interface/trans.c (constant_decl_with_initializer_p): New.
	(fold_constant_decl_in_expr): New function.
	(Identifier_to_gnu): Use constant_decl_with_initializer_p.
	For a constant renaming, try to fold a constant DECL in the result.
	(lvalue_required_p) <N_Object_Renaming_Declaration>: Always return 1.
	(Identifier_to_gnu): Reference the renamed object of constant renaming
	pointers directly.
	(Case_Statement_to_gnu): Do not re-fold the bounds of integer types.
	Assert that the case values are constant.
	* gcc-interface/utils.c (invalidate_global_renaming_pointers): Do not
	invalidate constant renaming pointers.

Co-Authored-By: Pierre-Marie de Rodat <derodat@adacore.com>

From-SVN: r209411