Give internal classes hidden visibility.

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

llvm-svn: 190534
diff --git a/llvm/lib/CodeGen/AllocationOrder.h b/llvm/lib/CodeGen/AllocationOrder.h
index aed461a..f0d35be 100644
--- a/llvm/lib/CodeGen/AllocationOrder.h
+++ b/llvm/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;