tcpreplay: Fix build on Mavericks by disabling builtin string fortify

tcpreplay provides its own support library for safe string operations,
which clashes with the macros in /usr/include/secure/_string.h

Same fix as MacPorts in http://trac.macports.org/ticket/41101

Partially closes #24572 (the issue of the second commenter, but not the original #24572 issue).