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