[llvm] [NFC][LLVM] Fix some `llvm` namespace usage in Bitcode writer (PR #141709)

[Rahul Joshi via llvm-commits]

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@@ -117,10 +118,6 @@ static cl::opt<bool>
 #endif
                                 cl::desc(""));
 
-namespace llvm {
-extern FunctionSummary::ForceSummaryHotnessType ForceSummaryEdgesCold;
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jurahul wrote:

Unfortunately, that does not work.  Note in the case below, llvm:: is for the type. Here we want to declare an extern variable in the llvm namespace, and `extern type llvm::VarName` does not work (I did try that first).

https://github.com/llvm/llvm-project/pull/141709