[llvm] [AMDGPU] Set SGPR spill stack IDs when creating spill slots (PR #197628)

[Matt Arsenault via llvm-commits]

================
@@ -0,0 +1,294 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -O1 -mtriple=amdgcn-amd-amdhsa -mcpu=gfx90a -verify-machineinstrs < %s | FileCheck %s
----------------
arsenm wrote:

```suggestion
; RUN: llc -O1 -mtriple=amdgcn-amd-amdhsa -mcpu=gfx90a < %s | FileCheck %s
```

https://github.com/llvm/llvm-project/pull/197628