[llvm] [AMDGPU] Rework architected SGPRs implementation (PR #79001)

[Matt Arsenault via llvm-commits]

================
@@ -143,6 +143,11 @@ struct AMDGPUFunctionArgInfo {
   ArgDescriptor WorkGroupInfo;
   ArgDescriptor PrivateSegmentWaveByteOffset;
 
+  // System TTMPs.
+  ArgDescriptor ArchitectedWorkGroupIDX;
----------------
arsenm wrote:

I don't think these really need to be tracked in ArgumentUsageInfo; they aren't arguments anymore 

https://github.com/llvm/llvm-project/pull/79001