fix: Patch coarsetime for MIPS AtomicU64 support

- Vendor coarsetime crate with portable-atomic fallback
- Use portable-atomic on targets without 64-bit atomics
- Patch crates.io to use local coarsetime
- Fixes MIPS build failure (AtomicU64 missing)

third_party/coarsetime/README.md

@@ -0,0 +1,90 @@
+[![Documentation](https://docs.rs/coarsetime/badge.svg)](https://docs.rs/coarsetime)
+[![Windows build status](https://ci.appveyor.com/api/projects/status/xlbhk9850dvl5ylh?svg=true)](https://ci.appveyor.com/project/jedisct1/rust-coarsetime)
+# coarsetime
+
+A Rust crate to make time measurements, that focuses on speed, API stability and portability.
+
+This crate is a partial replacement for the `Time` and `Duration` structures
+from the standard library, with the following differences:
+
+* Speed is privileged over accuracy. In particular, `CLOCK_MONOTONIC_COARSE` is
+used to retrieve the clock value on Linux systems, and transformations avoid
+operations that can be slow on non-Intel systems.
+* The number of system calls can be kept to a minimum. The "most recent
+timestamp" is always kept in memory. It can be read with just a load operation,
+and can be updated only as frequently as necessary.
+* The API is stable, and the same for all platforms. Unlike the standard library, it doesn't silently compile functions that do nothing but panic at runtime on some platforms.
+
+# Installation
+
+`coarsetime` is available on [crates.io](https://crates.io/crates/coarsetime)
+and works on Rust stable, beta, and nightly.
+
+Windows and Unix-like systems are supported.
+
+Available feature:
+
+* `wasi-abi2`: when targeting WASI, use the second preview of the ABI. Default is to use the regular WASI-core ABI.
+
+# Documentation
+
+[API documentation](https://docs.rs/coarsetime)
+
+# Example
+
+```rust
+extern crate coarsetime;
+
+use coarsetime::{Duration, Instant, Updater};
+
+// Get the current instant. This may require a system call, but it may also
+// be faster than the stdlib equivalent.
+let now = Instant::now();
+
+// Get the latest known instant. This operation is super fast.
+// In this case, the value will be identical to `now`, because we haven't
+// updated the latest known instant yet.
+let ts1 = Instant::recent();
+
+// Update the latest known instant. This may require a system call.
+// Note that a call to `Instant::now()` also updates the stored instant.
+Instant::update();
+
+// Now, we may get a different instant. This call is also super fast.
+let ts2 = Instant::recent();
+
+// Compute the time elapsed between ts2 and ts1.
+let elapsed_ts2_ts1 = ts2.duration_since(ts1);
+
+// Operations such as `+` and `-` between `Instant` and `Duration` are also
+// available.
+let elapsed_ts2_ts1 = ts2 - ts1;
+
+// Returns the time elapsed since ts1.
+// This retrieves the actual current time, and may require a system call.
+let elapsed_since_ts1 = ts1.elapsed();
+
+// Returns the approximate time elapsed since ts1.
+// This uses the latest known instant, and is super fast.
+let elapsed_since_recent = ts1.elapsed_since_recent();
+
+// Instant::update() should be called periodically, for example using an
+// event loop. Alternatively, the crate provides an easy way to spawn a
+// background task that will periodically update the latest known instant.
+// Here, the update will happen every 250ms.
+let updater = Updater::new(250).start().unwrap();
+
+// From now on, Instant::recent() will always return an approximation of the
+// current instant.
+let ts3 = Instant::recent();
+
+// Stop the task.
+updater.stop().unwrap();
+
+// Returns the elapsed time since the UNIX epoch
+let unix_timestamp = Clock::now_since_epoch();
+
+// Returns an approximation of the elapsed time since the UNIX epoch, based on
+// the latest time update
+let unix_timestamp_approx = Clock::recent_since_epoch();
+```