pal/solid: Implement SystemTime::{MIN, MAX}

This commit implements `SystemTime::MIN` and `SystemTime::MAX` for
solid.

The implementation uses a `time_t` to store the system time within a
single value (i.e. no dual secs/nanosecs handling), thereby implying its
`::MIN` and `::MAX` values as the respective boundaries.

Author: cvengler

library/std/src/sys/pal/solid/time.rs

@@ -10,6 +10,12 @@ pub struct SystemTime(abi::time_t);
 pub const UNIX_EPOCH: SystemTime = SystemTime(0);
 
 impl SystemTime {
+    #[unstable(feature = "time_systemtime_limits", issue = "none")]
+    pub const MAX: SystemTime = SystemTime(abi::time_t::MAX);
+
+    #[unstable(feature = "time_systemtime_limits", issue = "none")]
+    pub const MIN: SystemTime = SystemTime(abi::time_t::MIN);
+
     pub fn now() -> SystemTime {
         let rtc = unsafe {
             let mut out = MaybeUninit::zeroed();