[llvm] [llvm-exegesis] Begin replacing unsigned with MCRegister. NFC (PR #123109)

[Min-Yih Hsu via llvm-commits]

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@@ -47,9 +47,9 @@ Error SnippetGenerator::generateConfigurations(
   // using the scratch register and its aliasing registers.
   if (Variant.getInstr().hasMemoryOperands()) {
     const auto &ET = State.getExegesisTarget();
-    unsigned ScratchSpacePointerInReg =
+    MCRegister ScratchSpacePointerInReg =
         ET.getScratchMemoryRegister(State.getTargetMachine().getTargetTriple());
-    if (ScratchSpacePointerInReg == 0)
+    if (!ScratchSpacePointerInReg)
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mshockwave wrote:

`!ScratchSpacePointerInReg.isValid()`?

https://github.com/llvm/llvm-project/pull/123109