[clang] [clang][driver] Don't emit an error on an unrecognized SDK name (PR #181897)

[Cyndy Ishida via cfe-commits]

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@@ -2484,6 +2483,8 @@ void Darwin::AddDeploymentTarget(DerivedArgList &Args) const {
   // Read the SDKSettings.json file for more information, like the SDK version
   // that we can pass down to the compiler.
   SDKInfo = parseSDKSettings(getVFS(), Args, getDriver());
+  // FIXME: if SDKInfo is std::nullopt, diagnose a bad isysroot value (e.g.
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cyndyishida wrote:

The better docs are: https://llvm.org/docs/CodingStandards.html#source-code-formatting

https://github.com/llvm/llvm-project/pull/181897