std: Force `Instant::now()` to be monotonic

This commit is an attempt to force `Instant::now` to be monotonic
through any means possible. We tried relying on OS/hardware/clock
implementations, but those seem buggy enough that we can't rely on them
in practice. This commit implements the same hammer Firefox recently
implemented (noted in #56612) which is to just keep whatever the lastest
`Instant::now()` return value was in memory, returning that instead of
the OS looks like it's moving backwards.

Closes #48514
Closes #49281
cc #51648
cc #56560
Closes #56612
Closes #56940

1 files changed, 8 insertions, 0 deletions

diff --git a/src/libstd/sys/cloudabi/time.rs b/src/libstd/sys/cloudabi/time.rs
index 906beba4ae1..545e3c0ce84 100644
--- a/src/libstd/sys/cloudabi/time.rs
+++ b/src/libstd/sys/cloudabi/time.rs
@@ -25,6 +25,14 @@ impl Instant {
         }
     }
 
+    pub fn actually_monotonic() -> bool {
+        true
+    }
+
+    pub const fn zero() -> Instant {
+        Instant { t: 0 }
+    }
+
     pub fn sub_instant(&self, other: &Instant) -> Duration {
         let diff = self.t
             .checked_sub(other.t)