Use GetSystemTimePreciseAsFileTime if it is available

src/libstd/sys/windows/c.rs

@@ -1044,6 +1044,10 @@ pub fn SetFileInformationByHandle(_hFile: HANDLE,
                     _dwBufferSize: DWORD) -> BOOL {
         SetLastError(ERROR_CALL_NOT_IMPLEMENTED as DWORD); 0
     }
+    pub fn GetSystemTimePreciseAsFileTime(lpSystemTimeAsFileTime: LPFILETIME)
+                                          -> () {
+        GetSystemTimeAsFileTime(lpSystemTimeAsFileTime)
+    }
     pub fn SleepConditionVariableSRW(ConditionVariable: PCONDITION_VARIABLE,
                                      SRWLock: PSRWLOCK,
                                      dwMilliseconds: DWORD,

src/libstd/sys/windows/time.rs

@@ -74,7 +74,7 @@ impl SystemTime {
     pub fn now() -> SystemTime {
         unsafe {
             let mut t: SystemTime = mem::zeroed();
-            c::GetSystemTimeAsFileTime(&mut t.t);
+            c::GetSystemTimePreciseAsFileTime(&mut t.t);
             t
         }
     }