[clang] [llvm] [clang][CoverageMapping] Refactor when setting MC/DC True/False (PR #78202)

[NAKAMURA Takumi via cfe-commits]

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@@ -722,6 +709,12 @@ struct MCDCCoverageBuilder {
       return I->second;
   }
 
+  /// Return the LHS Decision ({0,0} if not set).
+  const DecisionIDPair &back() {
+    assert(DecisionStack.size() >= 1);
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chapuni wrote:

Dropped in the latest change. Thanks for pointing this out.

https://github.com/llvm/llvm-project/pull/78202