[COMMITTED] ada: Skip elaboration checks for abstract subprograms on derived types

["Marc Poulhiès" <poulhies@adacore.com>]

From: Piotr Trojanek <trojanek@adacore.com>

Elaboration checks skip abstract subprogram declarations, which have no
body that could be examined. Now these checks also skip abstract
subprograms of a derived type, which have no body either.

gcc/ada/

	* sem_elab.adb (Check_Overriding_Primitive): Prevent Corresponding_Body
	to be called with entity of an abstract subprogram.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/ada/sem_elab.adb | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/ada/sem_elab.adb b/gcc/ada/sem_elab.adb
index 1e18b987863..dc81e47da9e 100644
--- a/gcc/ada/sem_elab.adb
+++ b/gcc/ada/sem_elab.adb
@@ -15263,10 +15263,13 @@ package body Sem_Elab is
             --  Nothing to do for predefined primitives because they are
             --  artifacts of tagged type expansion and cannot override source
             --  primitives. Nothing to do as well for inherited primitives, as
-            --  the check concerns overriding ones.
+            --  the check concerns overriding ones. Finally, nothing to do for
+            --  abstract subprograms, because they have no body that could be
+            --  examined.
 
             if Is_Predefined_Dispatching_Operation (Prim)
               or else not Is_Overriding_Subprogram (Prim)
+              or else Is_Abstract_Subprogram (Prim)
             then
                return;
             end if;
-- 
2.40.0