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/RegAllocBase.h b/lib/CodeGen/RegAllocBase.h
index 597b1fc..9c00298 100644
--- a/lib/CodeGen/RegAllocBase.h
+++ b/lib/CodeGen/RegAllocBase.h
@@ -56,7 +56,7 @@
 /// Register allocators must override the selectOrSplit() method to implement
 /// live range splitting. They must also override enqueue/dequeue to provide an
 /// assignment order.
-class LLVM_LIBRARY_VISIBILITY RegAllocBase {
+class RegAllocBase {
 protected:
   const TargetRegisterInfo *TRI;
   MachineRegisterInfo *MRI;