Enable creating a const TimeSpec

Previously, there was no way to create a TimeSpec in a const context
because all creation was through traits. This adds two utility
functions to create a const TimeSpec from a libc::timespec or a
std::time::Duration

Author: danieldulaney

src/sys/time.rs

@@ -77,11 +77,7 @@ impl From<timespec> for TimeSpec {
 
 impl From<Duration> for TimeSpec {
     fn from(duration: Duration) -> Self {
-        #[cfg_attr(target_env = "musl", allow(deprecated))] // https://github.com/rust-lang/libc/issues/1848
-        TimeSpec(timespec {
-            tv_sec: duration.as_secs() as time_t,
-            tv_nsec: duration.subsec_nanos() as timespec_tv_nsec_t
-        })
+        Self::from_duration(duration)
     }
 }
 
@@ -198,6 +194,18 @@ impl TimeSpec {
     pub fn tv_nsec(&self) -> timespec_tv_nsec_t {
         self.0.tv_nsec
     }
+
+    pub const fn from_duration(duration: Duration) -> Self {
+        #[cfg_attr(target_env = "musl", allow(deprecated))] // https://github.com/rust-lang/libc/issues/1848
+        TimeSpec(timespec {
+            tv_sec: duration.as_secs() as time_t,
+            tv_nsec: duration.subsec_nanos() as timespec_tv_nsec_t
+        })
+    }
+
+    pub const fn from_timespec(timespec: timespec) -> Self {
+        Self(timespec)
+    }
 }
 
 impl ops::Neg for TimeSpec {