Handle std::sync::atomic::spin_loop_hint()
This PR adds support for `std::sync::atomic::spin_loop_hint()` by implementing the `llvm.x86.sse2.pause` intrinsic when the target is x86-based. It appears this is the first LLVM intrinsic in foreign_items, so I added a couple match blocks to handle it or fall through to the different OS-specific methods. I added a basic smoke test to `tests/run-pass/sync.rs`. I came across this by way of `crossbeam::utils::Backoff::spin()`, FWIW.
implement float_to_int_unchecked
@hanna-kruppe would be great if you could have a look at this.
`float.rs` tests legal casts. `test_cast` checks that both `as` casts and unchecked casts work (i.e., these are not saturating). The `compile-fail` tests should ensure that illegal casts via the intrinsic are detected as such.
Fixes https://github.com/rust-lang/miri/issues/1264
Implement `mach_timebase_info` for macOS
Since we return nanoseceonds instead of ticks from `mach_absolute_time`, we don't need to scale the absolute time
Fixes#1288
Add shims for RwLock::try_read/RwLock::try_write
This implements proper locking so that we can check for reentrancy and implement the `try_*` methods.
Fixes https://github.com/rust-lang/miri/issues/781
Add support for 'std::time::Instant' in Windows
Add support for creating `std::time::Instant` in Windows
Includes shims for `QueryPerformanceCounter` & `QueryPerformanceFrequency` in Windows, which are both called in Windows when `std::time::Instant` is created.
Windows docs page ["Acquiring high-resolution time stamps"](https://docs.microsoft.com/en-us/windows/win32/sysinfo/acquiring-high-resolution-time-stamps) was helpful in learning how `QueryPerformanceCounter` & `QueryPerformanceFrequency` work.
closes#1291
