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

[Alexandre Ganea via llvm-commits]

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@@ -107,6 +107,31 @@ void llvm::get_thread_name(SmallVectorImpl<char> &Name) {
 }
 
 SetThreadPriorityResult llvm::set_thread_priority(ThreadPriority Priority) {
+
+  typedef BOOL(WINAPI * SetThreadInformation_t)(
+      HANDLE hThread, THREAD_INFORMATION_CLASS ThreadInformationClass,
+      _In_reads_bytes_(ThreadInformationSize) PVOID ThreadInformation,
+      ULONG ThreadInformationSize);
+  static const auto pfnSetThreadInformation =
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aganea wrote:

We are already including `<processthreadsapi.h>` through `<windows.h>`. You don't need a function pointer here, you could use a static reference to the function.

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