[llvm] [LLVM][Clang][AArch64] Implement AArch64 build attributes (PR #123990)

[Nico Weber via llvm-commits]

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@@ -33,6 +33,7 @@ static_library("Support") {
     "Windows",
   ]
   sources = [
+    "AArch64BuildAttributes.cpp"
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nico wrote:

(fyi, there's no need to update .gn files. They're updated automatically by a bot based on changes to cmake files. if you do update them, please add trailing commas and add files just once instead of twice like here. i fixed this in 92b839e9c82450a3c465d349de73818e6aad59f3)

https://github.com/llvm/llvm-project/pull/123990