[llvm] [CodeGen] Rename RegisterMaskPair to RegUnitMaskPair. NFC (PR #123799)

[Craig Topper via llvm-commits]

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@@ -330,12 +330,11 @@ class LiveRegSet {
     return Regs.size();
   }
 
-  template<typename ContainerT>
-  void appendTo(ContainerT &To) const {
+  void appendTo(SmallVectorImpl<RegUnitMaskPair> &To) const {
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topperc wrote:

I removed the template here in favor of SmallVectorImpl&

https://github.com/llvm/llvm-project/pull/123799