Build fails with libpcap 1.9.0

[ryandesign]

Hello, tcpcrypt 0.5 builds fine for me on macOS High Sierra if I use the version of libpcap that ships with macOS in /usr.

However, if I try to use libpcap 1.9.0 as installed by MacPorts in /opt/local, then the build of tcpcrypt fails with:

libtool: link: ccache /usr/bin/clang -I./src -I./include -I./src -pipe -Os -arch x86_64 -Wall -Wno-deprecated-declarations -Wl,-headerpad_max_install_names -arch x86_64 -o src/tcpcryptd src/tcpcryptd-tcpcryptd.o src/tcpcryptd-tcpcrypt.o src/tcpcryptd-crypto.o src/tcpcryptd-crypto_aes.o src/tcpcryptd-crypto_hmac.o src/tcpcryptd-crypto_dummy.o src/tcpcryptd-profile.o src/tcpcryptd-checksum.o src/tcpcryptd-test.o src/tcpcryptd-crypto_hkdf.o src/tcpcryptd-crypto_reg.o src/tcpcryptd-crypto_ecdhe.o src/tcpcryptd-util.o shared/src_tcpcryptd-socket_address.o unix/src_tcpcryptd-priv.o src/tcpcryptd-freebsd.o src/tcpcryptd-unix.o  -L/opt/local/lib -lpcap -lcrypto -lpthread
Undefined symbols for architecture x86_64:
  "_pcap_set_filter_info", referenced from:
      _divert_open_pcap in tcpcryptd-unix.o
  "_pcap_set_want_pktap", referenced from:
      _divert_open_pcap in tcpcryptd-unix.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[1]: *** [src/tcpcryptd] Error 1