[llvm] Implement MCDCTVIdxBuilder (LLVM side) (PR #80676)

[NAKAMURA Takumi via llvm-commits]

================
@@ -557,6 +558,35 @@ struct MCDCRecord {
   }
 };
 
+/// Compute Conds[].Idx from Branch-like structure
+class MCDCTVIdxBuilder {
+public:
+  struct MCDCNode {
+    int InCount = 0; /// Reference count; temporary use
+    int Width;       /// Number of paths (>= 1)
----------------
chapuni wrote:

It was `W` in my prototype design. I have to update my imagination if this would be renamed.
Or, does the comment mislead?

https://github.com/llvm/llvm-project/pull/80676