The dl module seems to cause coredump on Pentium4 boxen when compiled
with gcc 3.3 with a -mcpu or -march flag (even -mcpu=pentiumpro, which
is the default CPU cflag that bsd.cpu.mk sets, leads ruby to coredump).
Although currently I'm not sure if gcc 3.3's optimization has a bug or
it is that it just exposed the dl module's hidden bug, disable those
flags to work around the problem for the moment.