[clang] [clang][driver][darwin] Prefer DarwinSDKInfo for platform identification and compatibility over the -isysroot path (PR #176541)

[Ian Anderson via cfe-commits]

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@@ -1382,26 +1382,61 @@ std::string Darwin::getCompilerRT(const ArgList &Args, StringRef Component,
   return std::string(FullPath);
 }
 
-StringRef Darwin::getPlatformFamily() const {
+static StringRef getPlatformFamily(Darwin::DarwinPlatformKind TargetPlatform) {
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ian-twilightcoder wrote:

This is a weird name. It's actually trying to get a prefix to match the SDK directory name on disk. It's only used if there isn't an SDKSettings.json file, so for old SDKs. It shouldn't need to be changed after this.

https://github.com/llvm/llvm-project/pull/176541