The current Makefile contains a bug here:

https://github.com/eggert/tz/blob/master/Makefile#L303

TZDSRCS= zdump.c localtime.c ialloc.c asctime.o
TZDOBJS= zdump.o localtime.o ialloc.o asctime.c

TZDSRCS should contain asctime.c and TZDOBJS should contain asctime.o. They're currently reversed.

-Andrew