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/SpillPlacement.h b/lib/CodeGen/SpillPlacement.h
index 0a90398..105516b 100644
--- a/lib/CodeGen/SpillPlacement.h
+++ b/lib/CodeGen/SpillPlacement.h
@@ -39,7 +39,7 @@
 class MachineBasicBlock;
 class MachineLoopInfo;
 
-class LLVM_LIBRARY_VISIBILITY SpillPlacement : public MachineFunctionPass {
+class SpillPlacement  : public MachineFunctionPass {
   struct Node;
   const MachineFunction *MF;
   const EdgeBundles *bundles;