[llvm] [clang] Hurd: Add x86_64 support (PR #78065)

[Fangrui Song via llvm-commits]

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@@ -2477,7 +2477,7 @@ void Generic_GCC::GCCInstallationDetector::AddDefaultGCCPrefixes(
       "x86_64-redhat-linux",    "x86_64-suse-linux",
       "x86_64-manbo-linux-gnu", "x86_64-linux-gnu",
       "x86_64-slackware-linux", "x86_64-unknown-linux",
-      "x86_64-amazon-linux"};
+      "x86_64-amazon-linux",    "x86_64-gnu"};
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MaskRay wrote:

There is a comment above that we should not add new elements to these arrays.

Is it here so that a target triple of `x86_64-pc-hurd-gnu` can find a GCC installation named `x86_64-gnu` for Debian? If that's the case, use code to indicate the special case for Hurd so that the logic will not affect other x86_64 OS triples.

https://github.com/llvm/llvm-project/pull/78065