[Ada] Do not analyze expression functions for dispatch tables

[Pierre-Marie de Rodat via Gcc-patches]

There is no need to analyze expression functions that are primitives of a
tagged type for its dispatch table because they will be analyzed at the end
of the current scope.

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

gcc/ada/

        * sem_attr.adb (Resolve_Attribute) <Attribute_Access>: Don't analyze
        the body of an expression function in the case of a dispatch table.
diff --git a/gcc/ada/sem_attr.adb b/gcc/ada/sem_attr.adb
--- a/gcc/ada/sem_attr.adb
+++ b/gcc/ada/sem_attr.adb
@@ -12144,11 +12144,15 @@ package body Sem_Attr is
                      elsif Scope (Subp_Id) /= Current_Scope then
                         null;
 
+                     --  Dispatch tables are not a freeze point either
+
+                     elsif Nkind (Parent (N)) = N_Unchecked_Type_Conversion
+                       and then Is_Dispatch_Table_Entity (Etype (Parent (N)))
+                     then
+                        null;
+
                       --  Analyze the body of the expression function to freeze
-                      --  the expression. This takes care of the case where the
-                      --  'Access is part of dispatch table initialization and
-                      --  the generated body of the expression function has not
-                      --  been analyzed yet.
+                      --  the expression.
 
                      else
                         Analyze (Subp_Body);