Revert "Give internal classes hidden visibility."

It works with clang, but GCC has different rules so we can't make all of those
hidden. This reverts commit r190534.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190536 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bitcode/Writer/ValueEnumerator.h

@@ -34,7 +34,7 @@ class ValueSymbolTable;
 class MDSymbolTable;
 class raw_ostream;
 
-class LLVM_LIBRARY_VISIBILITY ValueEnumerator {
+class ValueEnumerator {
 public:
   typedef std::vector<Type*> TypeList;