[clang] Silence an MSVC diagnostic; NFC (PR #220219)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman created https://github.com/llvm/llvm-project/pull/220219

This was emitting a "not all control paths return" diagnostic in MSVC

>From 9a4ccaee024c3d131202f654d4265f099c4169f5 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Tue, 1 Sep 2026 07:22:03 -0400
Subject: [PATCH] Silence an MSVC diagnostic; NFC

This was emitting a "not all control paths return" diagnostic in MSVC
---
 clang/lib/CodeGen/CGCall.cpp | 1 +
 1 file changed, 1 insertion(+)

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 63b07ae606353..1221829871b9f 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -129,6 +129,7 @@ unsigned CodeGenTypes::ClangCallConvToLLVMCallConv(CallingConv CC) {
     CC_VLS_CASE(65536)
 #undef CC_VLS_CASE
   }
+  llvm_unreachable("unhandled calling convention");
 }
 
 /// Derives the 'this' type for codegen purposes, i.e. ignoring method CVR