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

[Cyndy Ishida 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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cyndyishida wrote:

Can you write this comment at the top of this function? And/or actually change the name of the function as e.g. `getPrefixPlatformForSDK`

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