[clang] [clang][driver] Use platform specific calls to get the executable absolute path (PR #68091)

[Aaron Ballman via cfe-commits]

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@@ -331,6 +340,56 @@ static void SetInstallDir(SmallVectorImpl<const char *> &argv,
   // path being a symlink.
   SmallString<128> InstalledPath(argv[0]);
 
+#if defined(__linux__)
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AaronBallman wrote:

Can we use [`getMainExecutable()`](https://github.com/llvm/llvm-project/blob/1f0126902876cb42a7502047e62bdf512fd96b02/llvm/include/llvm/Support/FileSystem.h#L1345) instead?

(This sort of system-specific logic should live in LLVM's Support directory so that we don't sprinkle host-specific preprocessor conditionals all over, but better still if we can use our existing facilities rather than invent new ones.)

https://github.com/llvm/llvm-project/pull/68091