Fix libstd on DragonFly

Following changes:

* birthtime does not exist on DragonFly
* errno: __dfly_error is no more. Use #[thread_local] static errno.
* clock_gettime expects a c_ulong (use a type alias)

These changes are required to build DragonFly snapshots again.

src/libstd/os/dragonfly/fs.rs

@@ -63,10 +63,6 @@ pub trait MetadataExt {
     #[stable(feature = "metadata_ext2", since = "1.8.0")]
     fn st_ctime_nsec(&self) -> i64;
     #[stable(feature = "metadata_ext2", since = "1.8.0")]
-    fn st_birthtime(&self) -> i64;
-    #[stable(feature = "metadata_ext2", since = "1.8.0")]
-    fn st_birthtime_nsec(&self) -> i64;
-    #[stable(feature = "metadata_ext2", since = "1.8.0")]
     fn st_blksize(&self) -> u64;
     #[stable(feature = "metadata_ext2", since = "1.8.0")]
     fn st_blocks(&self) -> u64;
@@ -129,12 +125,6 @@ impl MetadataExt for Metadata {
     fn st_ctime_nsec(&self) -> i64 {
         self.as_inner().as_inner().st_ctime_nsec as i64
     }
-    fn st_birthtime(&self) -> i64 {
-        self.as_inner().as_inner().st_birthtime as i64
-    }
-    fn st_birthtime_nsec(&self) -> i64 {
-        self.as_inner().as_inner().st_birthtime_nsec as i64
-    }
     fn st_blksize(&self) -> u64 {
         self.as_inner().as_inner().st_blksize as u64
     }

src/libstd/sys/unix/os.rs

@@ -36,6 +36,7 @@ const TMPBUF_SZ: usize = 128;
 static ENV_LOCK: StaticMutex = StaticMutex::new();
 
 /// Returns the platform-specific value of errno
+#[cfg(not(target_os = "dragonfly"))]
 pub fn errno() -> i32 {
     extern {
         #[cfg_attr(any(target_os = "linux", target_os = "emscripten"),
@@ -47,7 +48,6 @@ pub fn errno() -> i32 {
                        target_env = "newlib"),
                    link_name = "__errno")]
         #[cfg_attr(target_os = "solaris", link_name = "___errno")]
-        #[cfg_attr(target_os = "dragonfly", link_name = "__dfly_error")]
         #[cfg_attr(any(target_os = "macos",
                        target_os = "ios",
                        target_os = "freebsd"),
@@ -60,6 +60,16 @@ pub fn errno() -> i32 {
     }
 }
 
+#[cfg(target_os = "dragonfly")]
+pub fn errno() -> i32 {
+    extern {
+        #[thread_local]
+        static errno: c_int;
+    }
+
+    errno as i32
+}
+
 /// Gets a detailed string description for the given error number.
 pub fn error_string(errno: i32) -> String {
     extern {

src/libstd/sys/unix/time.rs

@@ -303,8 +303,13 @@ mod inner {
         }
     }
 
+    #[cfg(not(target_os = "dragonfly"))]
+    pub type clock_t = libc::c_int;
+    #[cfg(target_os = "dragonfly")]
+    pub type clock_t = libc::c_ulong;
+
     impl Timespec {
-        pub fn now(clock: libc::c_int) -> Timespec {
+        pub fn now(clock: clock_t) -> Timespec {
             let mut t = Timespec {
                 t: libc::timespec {
                     tv_sec: 0,