Currently mailx uses some strange debian hackage to choose if it has to use -s in LDFLAGS or not... and by default it does.
The attached patch replaces the sed line currently used for EXTRAFLAGS (does it work actually? I haven't tried without my patch tbh) and allows to get a non-stripped copy of mailx (that can be passed through splitdebug).
This way it should also respect LDFLAGS correctly (again, haven't tried without, I'm just looking at the original makefile).
Created attachment 81739 [details, diff]
committed. thank you.