Rollup merge of #100984 - ChrisDenton:reinstate-init, r=Mark-Simulacrum

Reinstate preloading of some dll imports

I've now come around to the conclusion that there is a justification for pre-loading the synchronization functions `WaitOnAddress` and `WakeByAddressSingle`. I've found this to have a particularly impact in testing frameworks that may have short lived processes which immediately spawn lots of threads.

Also, because pre-main initializers imply a single-threaded environment, we can switch back to using relaxed atomics which might be a minor perf improvement on some platforms (though I doubt it's particularly notable).

r? ``@Mark-Simulacrum`` and sorry for the churn here.

For convenience I'll summarise previous issues with preloading and the solutions that are included in this PR (if any):

**Issue:** User pre-main initializers may be run before std's
**Solution:** The std now uses initializers that are guaranteed to run earlier than the old initializers. A note is also added that users should not copy std's behaviour if they want to ensure they run their initializers after std.

**Issue:** Miri does not understand pre-main initializers.
**Solution:** For miri only, run the function loading lazily instead.

**Issue:** We should ideally use `LoadLibrary` to get "api-ms-win-core-synch-l1-2-0". Only "ntdll" and "kernel32" are guaranteed to always be loaded.
**Solution:** None. We can't use `LoadLibrary` pre-main. However, in the past `GetModuleHandle` has always worked in practice so this should hopefully not be a problem.

If/when Windows 7 support is dropped, we can finally remove all this for good and just use normal imports.

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