[PATCH v13 0/4] MR741: ntdll: Implement NtFlushProcessWriteBuffers.

[Torge Matthies (＠tmatthies)]

Based on [a patch](https://www.winehq.org/mailman3/hyperkitty/list/wine-devel(a)winehq.org/mess...) by Jinoh Kang (@iamahuman) from February 2022.

I removed the need for the event object and implemented fast paths for Linux.  
On macOS 10.14+ `thread_get_register_pointer_values` is called on every thread of the process.  
On Linux 4.14+ `membarrier(MEMBARRIER_CMD_GLOBAL_EXPEDITED, ...)` is used.  
On x86 Linux <= 4.13 and on other platforms `madvise(..., MADV_DONTNEED)` is used, which sends IPIs to all cores causing them to do a memory barrier.

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  v13: ntdll/tests: Add basic NtFlushProcessWriteBuffers test.
 
https://gitlab.winehq.org/wine/wine/-/merge_requests/741