[CodeGen] Reduce visibility of implementation details

NFC.

llvm-svn: 241164
diff --git a/llvm/lib/CodeGen/LiveDebugVariables.h b/llvm/lib/CodeGen/LiveDebugVariables.h
index ac2d1a1..694aa17 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.h
+++ b/llvm/lib/CodeGen/LiveDebugVariables.h
@@ -31,7 +31,7 @@
 class LiveIntervals;
 class VirtRegMap;
 
-class LiveDebugVariables : public MachineFunctionPass {
+class LLVM_LIBRARY_VISIBILITY LiveDebugVariables : public MachineFunctionPass {
   void *pImpl;
   DenseMap<const Function *, DISubprogram *> FunctionDIs;