On Mac OS 10.9.5:

    cc conkeror.git/conkeror-spawn-helper.c -o Conkeror.app/Contents/MacOS/conkeror/conkeror-spawn-helper
    conkeror.git/conkeror-spawn-helper.c:122:24: warning: implicit declaration of function 'inet_addr' is
invalid in C99
          [-Wimplicit-function-declaration]
      sa.sin_addr.s_addr = inet_addr("127.0.0.1");
                       ^
1 warning generated.

The fix is to

    #include <arpa/inet.h>

I hesitate to suggest a patch b/c I don't have other OSs to test on.

Compiler is

Apple LLVM version 6.0 (clang-600.0.51) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin13.4.0
Thread model: posix