Give internal classes hidden visibility.

Worth 100k on a linux/x86_64 Release+Asserts clang.

llvm-svn: 190534
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
index ecffb25..2a8b648 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
@@ -34,7 +34,7 @@
 //===----------------------------------------------------------------------===//
 /// CompileUnit - This dwarf writer support class manages information associated
 /// with a source file.
-class CompileUnit {
+class LLVM_LIBRARY_VISIBILITY CompileUnit {
   /// UniqueID - a numeric ID unique among all CUs in the module
   ///
   unsigned UniqueID;