unix fs: Make hurd and horizon using explicit new rather than From

408c0ea ("unix time module now return result") dropped the From
impl for SystemTime, breaking the hurd and horizon builds.

Fixes rust-lang#123032

(cherry picked from commit 7b4e507)

library/std/src/sys/pal/unix/fs.rs

@@ -517,7 +517,7 @@ impl FileAttr {
 
     #[cfg(any(target_os = "horizon", target_os = "hurd"))]
     pub fn modified(&self) -> io::Result<SystemTime> {
-        Ok(SystemTime::from(self.stat.st_mtim))
+        SystemTime::new(self.stat.st_mtim.tv_sec as i64, self.stat.st_mtim.tv_nsec as i64)
     }
 
     #[cfg(not(any(
@@ -545,7 +545,7 @@ impl FileAttr {
 
     #[cfg(any(target_os = "horizon", target_os = "hurd"))]
     pub fn accessed(&self) -> io::Result<SystemTime> {
-        Ok(SystemTime::from(self.stat.st_atim))
+        SystemTime::new(self.stat.st_atim.tv_sec as i64, self.stat.st_atim.tv_nsec as i64)
     }
 
     #[cfg(any(