Building with GNU extensions will work:
CC=gcc CFLAGS="-std=gnu89" make check OK (4 tests, 4 assertions).
CC=gcc CFLAGS="-std=c89" make check make: *** [Makefile:6: check] Error 1
Produces a variety of errors. Some seem to be caused by
CLOCK_MONOTONIC and other time related functions/macros/constants not being pulled in.