Auto merge of #3394 - devnexen:dflybsd_getmntinfo, r=JohnTitor

adding getmntinfo/getmntvinfo for DragonFlyBSD.

close #3392

Author: bors

libc-test/semver/dragonfly.txt

@@ -1320,6 +1320,8 @@ getitimer
 getlastlogx
 getline
 getloadavg
+getmntinfo
+getmntvinfo
 getnameinfo
 getopt_long
 getpeereid

src/unix/bsd/freebsdlike/dragonfly/mod.rs

@@ -1678,6 +1678,12 @@ extern "C" {
 
     pub fn dirname(path: *mut ::c_char) -> *mut ::c_char;
     pub fn basename(path: *mut ::c_char) -> *mut ::c_char;
+    pub fn getmntinfo(mntbufp: *mut *mut ::statfs, flags: ::c_int) -> ::c_int;
+    pub fn getmntvinfo(
+        mntbufp: *mut *mut ::statfs,
+        mntvbufp: *mut *mut ::statvfs,
+        flags: ::c_int,
+    ) -> ::c_int;
 }
 
 #[link(name = "rt")]