$ cat Makefile

rulea:
    @echo rulea

ruleb:
    @echo ruleb
    pass = $(shell openssl passwd -1)

rulec:
ifeq ($(SPL_VAR),)
    $(error "SPL_VAR undefined, aborting")
else
    @echo rulec
endif

.PHONY: rulea ruleb rulec

$ make rulea
Makefile:10: *** "SPL_VAR undefined, aborting".  Stop.

$ make -v
GNU Make 4.1
Built for x86_64-pc-linux-gnu

$ uname -a
Linux thinkpad 4.13.0-38-generic #43~16.04.1-Ubuntu SMP Wed Mar 14 17:48:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux