Stop gdb in gnat_runtime_has_debug_info

gnat_runtime_has_debug_info starts a new gdb to do its work.  However,
it also leaves this gdb running, which can potentially confuse the
calling test -- I encountered this when writing a new DAP test.  This
patch changes the proc to shut down gdb.



diff --git a/gdb/testsuite/lib/ada.exp b/gdb/testsuite/lib/ada.exp
index b728e3a..b4a93fa 100644
--- a/gdb/testsuite/lib/ada.exp
+++ b/gdb/testsuite/lib/ada.exp
@@ -204,5 +204,7 @@
 	}
     }
 
+    gdb_exit
+
     return $has_debug_info
 }