[llvm] Move a lot of symbol code to use the symbol string pool (PR #115796)

[Jared Wyles via llvm-commits]

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@@ -434,27 +437,45 @@ class Symbol {
     setTargetFlags(TargetFlagsType{});
   }
 
+  static Symbol &constructCommon(BumpPtrAllocator &Allocator, Block &Base,
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jaredwy wrote:

looks like i added this back in. Ill delete it just let the build bots currently running finish to see if there are any other issues. 

https://github.com/llvm/llvm-project/pull/115796