subprocesses.adb: Do not set the exit status when ignoring subcommand failure

Change the verbose reporting mechanism for Run_Command when ignoring subprocess
failures to not set the exit status of gnatcov to Failure, as it otherwise
defeats the point of ignoring the failures.

Author: leocreuse

tools/gnatcov/subprocesses.adb

@@ -106,7 +106,11 @@ package body Subprocesses is
          if Success then
             Put_Line (Command & " finished");
          else
-            Error (Origin_Command_Name & " failed");
+            --  Do not use Error as this sets the exit status to Failure, but
+            --  here we are precisely ignoring the fact that the subprocess
+            --  failed.
+
+            Warning_Or_Error (Origin_Command_Name & " failed");
          end if;
       end if;
    end Check_Status;