Warning when compiling s-interr.adb runtime file with -gnatc

[David Sauvage <sauvage.david@gmail.com>]

When compiling s-interr.adb runtime file with -gnatc [1] produce a
warning [2]. This warning is not raise when compiling wihtout -gnatc.

Does the target and source types [3] really have different sizes ? or
may be it's a problem on gnat ?

[1]
-gnatc    Check syntax and semantics only (no code generation)

[2]
$ gcc-4.3 -c -gnatpg -nostdinc -nostdlib -g -gnatc -I- -gnatA /usr/lib/
gcc/i486-linux-gnu/4.3.2/rts-native/adainclude/s-interr.adb -I/usr/lib/
gcc/i486-linux-gnu/4.3.2/rts-native/adainclude/
s-interr.adb:569:07: warning: types for unchecked conversion have
different sizes

[3]
s-interr.ads
   type Parameterless_Handler is access protected procedure;
s-interr.adb
   564	      type Fat_Ptr is record
   565	         Object_Addr  : System.Address;
   566	         Handler_Addr : System.Address;
   567	      end record;
   568
   569	      function To_Fat_Ptr is new Ada.Unchecked_Conversion
   570	        (Parameterless_Handler, Fat_Ptr);

Ubuntu Intrepid x86
libgnat-4.3 (4.3.2-1ubuntu1)