errors on Mac OS

[jmonster]

bundle exec rake

cd tmp/x86_64-darwin13.0/rankable_graph/2.1.3
make
compiling ../../../../ext/rankable_graph/rankable_graph.c
../../../../ext/rankable_graph/rankable_graph.c:97:14: error: static declaration of 'link' follows non-static declaration
static VALUE link(VALUE self, VALUE from, VALUE to){
             ^
/usr/include/unistd.h:458:6: note: previous declaration is here
int      link(const char *, const char *);
         ^
../../../../ext/rankable_graph/rankable_graph.c:236:47: warning: incompatible pointer types passing 'int (const char *, const char *)' to parameter of type 'VALUE (*)()' [-Wincompatible-pointer-types]
  rb_define_method(rb_cRankableGraph, "link", link, 2);
                                              ^~~~
/Users/jmonster/.rbenv/versions/2.1.3/include/ruby-2.1.0/ruby/ruby.h:1400:48: note: passing argument to parameter here
void rb_define_method(VALUE,const char*,VALUE(*)(ANYARGS),int);
                                               ^
1 warning and 1 error generated.
make: *** [rankable_graph.o] Error 1
rake aborted!
Command failed with status (2): [make...]

Tasks: TOP => default => spec => compile => compile:x86_64-darwin13.0 => compile:rankable_graph:x86_64-darwin13.0 => copy:rankable_graph:x86_64-darwin13.0:2.1.3 => tmp/x86_64-darwin13.0/rankable_graph/2.1.3/rankable_graph.bundle
``