[llvm] Windows: use EcoQoS for ThreadPriority::Background (PR #148797)

[Alexandre Ganea via llvm-commits]

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@@ -107,6 +107,39 @@ void llvm::get_thread_name(SmallVectorImpl<char> &Name) {
 }
 
 SetThreadPriorityResult llvm::set_thread_priority(ThreadPriority Priority) {
+
+  // SetThreadInformation is only available on Windows 8 and later. so we load
+  // it at run-time
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aganea wrote:

Can you please mention explicitely that we want to keep compatibility with Windows 7?

https://github.com/llvm/llvm-project/pull/148797