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

[Liviu Ionescu 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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ilg-ul wrote:

> Can we use `getMainExecutable()` instead?

Good point! 

> So is the problem here that SetInstallDir is called after the above (having constructed TheDriver). Resulting in InstalledDir being changed into being relative to the symlink?

When I first encountered this problem I tried to run a debug session to understand how things work, but got confused and in the end I patched `SetInstallDir` and for my needs it was ok, but since `getMainExecutable()` already does the job I'll reconsider and try to understand where the problem comes from.

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