[llvm] CodeGen: Add RegisterClass by HwMode (PR #158269)

[Matt Arsenault via llvm-commits]

================
@@ -259,6 +259,7 @@ class LLVM_ABI MCSubtargetInfo {
     HwMode_ValueType, // Return the HwMode ID that controls the ValueType.
     HwMode_RegInfo,   // Return the HwMode ID that controls the RegSizeInfo and
                       // SubRegRange.
+    HwMode_RegClass,  // Return the HwMode ID that controls the RegisterClass.
----------------
arsenm wrote:

I'm not really sure. The distinct HwMode types seems like a half-implemented API change. Everywhere else just uses the default value, which only seems to differ by an assertion 

https://github.com/llvm/llvm-project/pull/158269