Give internal classes hidden visibility.

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190534 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AllocationOrder.h b/lib/CodeGen/AllocationOrder.h
index aed461a..f0d35be 100644
--- a/lib/CodeGen/AllocationOrder.h
+++ b/lib/CodeGen/AllocationOrder.h
@@ -25,7 +25,7 @@
 class RegisterClassInfo;
 class VirtRegMap;
 
-class AllocationOrder {
+class LLVM_LIBRARY_VISIBILITY AllocationOrder {
   SmallVector<MCPhysReg, 16> Hints;
   ArrayRef<MCPhysReg> Order;
   int Pos;