Auto merge of #482 - MrFloya:initgroups, r=alexcrichton

Added initgroups

Not sure whether this is the correct platform level. I'll wait for CI to find out..

EDIT: Okay now it builds on all platforms but I think this configuration does not add the function on BSD where it has the same signature as on Linux.

Author: bors

src/unix/bsd/apple/mod.rs

@@ -1530,6 +1530,8 @@ extern {
                     linkpath: *const ::c_char) -> ::c_int;
    pub fn unlinkat(dirfd: ::c_int, pathname: *const ::c_char,
                    flags: ::c_int) -> ::c_int;
+
+    pub fn initgroups(user: *const ::c_char, basegroup: ::c_int) -> ::c_int;
 }
 
 cfg_if! {

src/unix/notbsd/mod.rs

@@ -738,6 +738,7 @@ extern {
     pub fn memalign(align: ::size_t, size: ::size_t) -> *mut ::c_void;
     pub fn setgroups(ngroups: ::size_t,
                      ptr: *const ::gid_t) -> ::c_int;
+    pub fn initgroups(user: *const ::c_char, group: ::gid_t) -> ::c_int;
     pub fn sched_setscheduler(pid: ::pid_t,
                               policy: ::c_int,
                               param: *const sched_param) -> ::c_int;