[clang] [clang][AIX] Handle triple environment component for per target runtime directory (PR #140850)

[Jake Egan via cfe-commits]

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@@ -935,6 +935,14 @@ ToolChain::getTargetSubDirPath(StringRef BaseDir) const {
   if (auto Path = getPathForTriple(T))
     return *Path;
 
+  // On AIX, the environment component is not used in the target sub dir name.
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jakeegan wrote:

`getTripleWithoutOSVersion` seems to preserve the trailing -unknown component. I considered modifying it to strip that too, but that would do more than what the name of the function implies. I could add `T.isOSAIX()` to that block as you said if we're fine with modifying `getTripleWithoutOSVersion` to strip `-unknown` too. 

https://github.com/llvm/llvm-project/pull/140850