Added freebsd config for PCRE

mmmagic fails to compile on FreeBSD due to a missing config file for pcre.

    CC(target) Release/obj.target/libpcre/deps/libmagic/pcre/pcre_byte_order.o
    ../deps/libmagic/pcre/pcre_byte_order.c:47:20: error: config.h: No such file or directory
    gmake: *** [Release/obj.target/libpcre/deps/libmagic/pcre/pcre_byte_order.o] Error 1

This patch adds the necessary config file.