[clang] [flang] [llvm] Add IR Profile-Guided Optimization (IR PGO) support to the Flang compiler (PR #136098)

[Tarun Prabhu via cfe-commits]

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@@ -19,6 +21,7 @@ template <typename T> class Expected;
 template <typename T> class IntrusiveRefCntPtr;
 class Module;
 class MemoryBufferRef;
+extern cl::opt<llvm::PGOOptions::ColdFuncOpt> ClPGOColdFuncAttr;
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tarunprabhu wrote:

Since this is an experimental option that will likely be removed and is only to be used in BackendUtil.cpp, it is better to move it there. Essentially, what was originally the `static` definition of `ClPGOColdFuncAttr` in `BackendUtil.cpp` would become `extern ClPGOColdFuncAttr`.

https://github.com/llvm/llvm-project/pull/136098