[m-rev.] diff: Fix decode_system_command_exit_code returning negative signal numbers.

[Peter Wang]

library/io.call_system.m:
    As above.

diff --git a/library/io.call_system.m b/library/io.call_system.m
index 2f11b417d..d1144204c 100644
--- a/library/io.call_system.m
+++ b/library/io.call_system.m
@@ -316,7 +316,7 @@ decode_system_command_exit_code(Code0) = Status :-
             Status = WEXITSTATUS(Status0);
         } else if (WIFSIGNALED(Status0)) {
             Signalled = MR_YES;
-            Signal = -WTERMSIG(Status0);
+            Signal = WTERMSIG(Status0);
         }
     #else
         Exited = MR_YES;
-- 
2.31.0