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
Add support for OpenOptions::create_new()/O_EXCL
This PR extends the POSIX shim for `open` to support the `O_EXCL` flag, when it is used alongside `O_CREAT`, and exercises it by testing `OpenOptions::create_new`.
Environ shim
Remake of https://github.com/rust-lang/miri/pull/1147. There are three main problems with this:
1. For some reason `update_environ` is not updating `environ` when `setenv` or `unsetenv` are called. Even then it works during initialization.
2. I am not deallocating the old array with the variables in `update_environ`.
3. I had to store the `environ` place into `MemoryExtra` as a field to update it. I was thinking about changing `extern_statics` to store places instead of `AllocID`s to avoid this.
@RalfJung
Add directory-related shims
This PR adds support for `mkdir`, `rmdir`, `opendir`, `closedir`, and `readdir64_r`.
Open directory streams are tracked through a HashMap indexed by pointer locations, which holds directory iterators. Since `DIR` is an opaque type in glibc, I represent them with 1-byte allocations, and then just use their pointers in HashMap lookups.
Tests are included to exercise the new functionality.
