Seems ld doesn't play well with -z option on OSX

This should fix issue #11 (partially, at least). Error is:
    [...]
    cc -Wall -Werror -Wextra -Qunused-arguments -DPROGNAME=\"dislocker\"
    -DVERSION=\"0.3.1\" -D_FILE_OFFSET_BITS=64 -DAUTHOR="\"Romain
    Coltel\"" -D__OS=\"Darwin\" -D__ARCH=\"x86_64\" -D__ARCH_X86_64
    -D__DARWIN -I. -I/usr/local/include -fstack-protector -fPIC
    -D_FORTIFY_SOURCE=2 -O1 -D__RUN_FUSE -DFUSE_USE_VERSION=26 -o
    dislocker dislocker.o common.o sectors.o config.o xstd/xstdio.o
    xstd/xstdlib.o outputs/prepare.o outputs/fuse/fuse.o
    metadata/datums.o metadata/metadata.o metadata/print_metadata.o
    metadata/vmk.o metadata/fvek.o metadata/extended_info.o
    metadata/guid.o accesses/rp/recovery_password.o
    accesses/bek/read_bekfile.o accesses/user_pass/user_pass.o
    accesses/stretch_key.o encryption/decrypt.o encryption/encrypt.o
    encryption/diffuser.o encryption/crc32.o ntfs/clock.o
    ntfs/encoding.o  -pie -fPIE -Wl,-z,relro -Wl,-z,now -lpthread
    -lpolarssl -losxfuse_i64
    ld: unknown option: -z
The commit removes -Wl,-z,* from command under Darwin.