[llvm] [llvm-cov] Fix MSVC "not all control paths return a value" warning. NFC. (PR #161150)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon created https://github.com/llvm/llvm-project/pull/161150

None

>From 95f394f619316b8013549d7aeb6a9ebc941f904c Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev at redking.me.uk>
Date: Mon, 29 Sep 2025 09:41:27 +0100
Subject: [PATCH] [llvm-cov] Fix MSVC "not all control paths return a value"
 warning. NFC.

---
 llvm/tools/llvm-cov/CoverageExporterJson.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/llvm/tools/llvm-cov/CoverageExporterJson.cpp b/llvm/tools/llvm-cov/CoverageExporterJson.cpp
index ff86c8dfe951b..4c07c05396732 100644
--- a/llvm/tools/llvm-cov/CoverageExporterJson.cpp
+++ b/llvm/tools/llvm-cov/CoverageExporterJson.cpp
@@ -118,6 +118,7 @@ json::Value renderCondState(const coverage::MCDCRecord::CondState CondState) {
   case coverage::MCDCRecord::MCDC_False:
     return json::Value(false);
   }
+  llvm_unreachable("Unknown llvm::coverage::MCDCRecord::CondState enum");
 }
 
 json::Array gatherTestVectors(coverage::MCDCRecord &Record) {