Auto merge of #537 - Susurrus:master, r=alexcrichton

Add ppoll() for all unix platforms

I'm unsure of whether there is support in OS X for this, and I can't find anything online (so I'm betting there isn't), but I'm going to let this run through CI to confirm.

Author: bors

src/unix/bsd/freebsdlike/mod.rs

@@ -950,6 +950,10 @@ extern {
     pub fn pthread_mutex_timedlock(lock: *mut pthread_mutex_t,
                                    abstime: *const ::timespec) -> ::c_int;
     pub fn pipe2(fds: *mut ::c_int, flags: ::c_int) -> ::c_int;
+    pub fn ppoll(fds: *mut ::pollfd,
+                 nfds: ::nfds_t,
+                 timeout: *const ::timespec,
+                 sigmask: *const sigset_t) -> ::c_int;
 }
 
 cfg_if! {

src/unix/notbsd/mod.rs

@@ -841,6 +841,10 @@ extern {
                      linkpath: *const ::c_char) -> ::c_int;
     pub fn unlinkat(dirfd: ::c_int, pathname: *const ::c_char,
                     flags: ::c_int) -> ::c_int;
+    pub fn ppoll(fds: *mut ::pollfd,
+                 nfds: nfds_t,
+                 timeout: *const ::timespec,
+                 sigmask: *const sigset_t) -> ::c_int;
     pub fn pthread_condattr_getclock(attr: *const pthread_condattr_t,
                                      clock_id: *mut clockid_t) -> ::c_int;
     pub fn pthread_condattr_setclock(attr: *mut pthread_condattr_t,