Give internal classes hidden visibility.

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

llvm-svn: 190534
diff --git a/llvm/lib/Bitcode/Writer/ValueEnumerator.h b/llvm/lib/Bitcode/Writer/ValueEnumerator.h
index d1ca15f..f208eb3 100644
--- a/llvm/lib/Bitcode/Writer/ValueEnumerator.h
+++ b/llvm/lib/Bitcode/Writer/ValueEnumerator.h
@@ -34,7 +34,7 @@
 class MDSymbolTable;
 class raw_ostream;
 
-class ValueEnumerator {
+class LLVM_LIBRARY_VISIBILITY ValueEnumerator {
 public:
   typedef std::vector<Type*> TypeList;