[llvm] Fix compiler errors in GVN.h for clang versions older than 15 (PR #107636)

[Thomas Fransham via llvm-commits]

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@@ -130,7 +130,12 @@
 
 #if (!(defined(_WIN32) || defined(__CYGWIN__)) ||                              \
      (defined(__MINGW32__) && defined(__clang__)))
+// Clang compilers older then 15 do not support gnu style attributes on namespaces
+#if defined(__clang__) && _clang_major__ < 15
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fsfod wrote:

I guess i should of read further down when i went looking for the correct macro on this page https://github.com/cpredef/predef/blob/master/Compilers.md#clang

https://github.com/llvm/llvm-project/pull/107636