[CodeGen] Reduce visibility of implementation details

NFC.

llvm-svn: 241164
diff --git a/llvm/lib/CodeGen/BranchFolding.h b/llvm/lib/CodeGen/BranchFolding.h
index 3653a2c..46c05dc 100644
--- a/llvm/lib/CodeGen/BranchFolding.h
+++ b/llvm/lib/CodeGen/BranchFolding.h
@@ -24,7 +24,7 @@
   class TargetInstrInfo;
   class TargetRegisterInfo;
 
-  class BranchFolder {
+  class LLVM_LIBRARY_VISIBILITY BranchFolder {
   public:
     explicit BranchFolder(bool defaultEnableTailMerge, bool CommonHoist,
                           const MachineBlockFrequencyInfo &MBFI,