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

[Teresa Johnson 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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teresajohnson wrote:

I suppose this could be simplified to "extern llvm::FunctionSummary::..." like the extern llvm::cl::opt below, if we decide to keep it.

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