The configure check for -Wformat-security is broken because it checks the flags one-by-one, but -Wformat-security only works together with -Wformat:
configure:15548: checking if gcc -std=gnu99 supports flag -Wformat-security in envvar CFLAGS
configure:15559: gcc -std=gnu99 -c -Werror -Wformat-security conftest.c >&5
cc1: error: -Wformat-security ignored without -Wformat [-Werror=format-security]
cc1: all warnings being treated as errors
configure:15559: $? = 1
I think this broke in commit eb2e280f9c59b66965c9316eadc4c113a13ca744 ; prior to that commit, the flags were appended to CFLAGS directly and there is a check for -Wformat=2 before the -Wformat-security check.
systemd is git master, gcc is gcc (GCC) 4.7.2 20120921 (Red Hat 4.7.2-2)
Just combined the format options into one argument for now. Thanks!