[clang] [clang][driver][darwin] Report bad SDKSettings as a fatal error rather than unreachable (PR #175073)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Ian Anderson (ian-twilightcoder)

<details>
<summary>Changes</summary>

Fatal error is more appropriate than unreachable when the SDKSettings is not in a recognized form (encountered in a few tests with incomplete SDKSettings.json).

---
Full diff: https://github.com/llvm/llvm-project/pull/175073.diff


1 Files Affected:

- (modified) clang/lib/Basic/DarwinSDKInfo.cpp (+3-1) 


``````````diff
diff --git a/clang/lib/Basic/DarwinSDKInfo.cpp b/clang/lib/Basic/DarwinSDKInfo.cpp
index 4fd31b841b23d..b55ffd1c39a86 100644
--- a/clang/lib/Basic/DarwinSDKInfo.cpp
+++ b/clang/lib/Basic/DarwinSDKInfo.cpp
@@ -112,7 +112,9 @@ parsePlatformInfos(const llvm::json::Object &Obj, VersionTuple Version) {
                                llvm::Triple::UnknownEnvironment,
                                llvm::Triple::MachO, "/System/DriverKit"});
     } else {
-      llvm_unreachable("Unrecognized Xcode platform");
+      llvm::reportFatalUsageError(
+          "Unrecognized CanonicalName in SDKSettings.json. SupportedTargets is "
+          "expected, or a recognized CanonicalName.");
     }
     return PlatformInfos;
   }

``````````

</details>


https://github.com/llvm/llvm-project/pull/175073