build-sys: silence non-POSIX variable name warning
Easiest way to get rid of the following warning is to ignore the warning.
This might cause people who use non-GNU make to have hard time, but are
there such people compiling this project?
sys-utils/Makemodule.am:226: warning: addprefix sys-utils/,$(SETARCH_LINKS: non-POSIX variable name
sys-utils/Makemodule.am:226: (probably a GNU make extension)