command "lin-lwp" is defined in linux-nat.c, so for GDB without
linux-nat.o, command "set debug lin-lwp 1" can't be found, like this:

set debug lin-lwp 1^M
Undefined set debug command: "lin-lwp 1".  Try "help set debug".^M
(gdb) FAIL: gdb.threads/ia64-sigill.exp: set debug lin-lwp 1

I examine the test code, and comment says "The ia64 SIGILL signal is
visible only in the lin-lwp debug.", however, I don't see any code
checks the lin-lwp debug output.  I think this line of code "set debug
lin-lwp 1" can be removed from this test case.

OK?

-- 
Yao (齐尧)