[Ada] Spurious accessibility error on allocator

[Pierre-Marie de Rodat <derodat@adacore.com>]

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This patch fixes an error in the compiler whereby an allocator for a
limited type may cause spurious accessibility errors due to a
miscalculation of access levels on interally generated temporaries.

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

gcc/ada/

	* exp_ch6.adb (Make_Build_In_Place_Call_Allocator): Normalize
	the associated node for internally generated objects to be like
	their SOAAT counter-parts.

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diff --git a/gcc/ada/exp_ch6.adb b/gcc/ada/exp_ch6.adb
--- a/gcc/ada/exp_ch6.adb
+++ b/gcc/ada/exp_ch6.adb
@@ -9732,6 +9732,12 @@ package body Exp_Ch6 is
                     New_Occurrence_Of (Etype (BIP_Func_Call), Loc),
                   Expression   => New_Copy_Tree (BIP_Func_Call))));
 
+      --  Manually set the associated node for the anonymous access type to
+      --  be its local declaration to avoid confusing and complicating
+      --  the accessibility machinary.
+
+      Set_Associated_Node_For_Itype (Anon_Type, Tmp_Decl);
+
       Expander_Mode_Save_And_Set (False);
       Insert_Action (Allocator, Tmp_Decl);
       Expander_Mode_Restore;