Add tcfgetsid for all unices

src/unix/mod.rs

@@ -863,6 +863,7 @@ extern {
                      termios: *const ::termios) -> ::c_int;
     pub fn tcflow(fd: ::c_int, action: ::c_int) -> ::c_int;
     pub fn tcflush(fd: ::c_int, action: ::c_int) -> ::c_int;
+    pub fn tcgetsid(fd: ::c_int) -> ::pid_t;
     pub fn tcsendbreak(fd: ::c_int, duration: ::c_int) -> ::c_int;
     pub fn mkstemp(template: *mut ::c_char) -> ::c_int;
     pub fn mkdtemp(template: *mut ::c_char) -> *mut ::c_char;