[clang] [docs] alias attribute doc (PR #193652)

[Kartik Ohlan via cfe-commits]

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@@ -9983,3 +9983,26 @@ different languages to coexist on the same call stack while each interpreting
 exceptions according to their own rules.
   }];
 }
+
+def AliasDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``alias`` attribute causes the declaration to be emitted as an alias to
+another symbol, which must be defined in the same translation unit.
+
+The attribute can be applied to both functions and global variables. 
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Ko496-glitch wrote:

@AaronBallman i also tried to find this in gcc issue tracker but was unfortunate. Do you suggest opening an issue in gcc ?

https://github.com/llvm/llvm-project/pull/193652