Make headers self-contained again.

llvm-svn: 262702
diff --git a/llvm/lib/Target/X86/X86SelectionDAGInfo.h b/llvm/lib/Target/X86/X86SelectionDAGInfo.h
index 5a5fd91..828243c 100644
--- a/llvm/lib/Target/X86/X86SelectionDAGInfo.h
+++ b/llvm/lib/Target/X86/X86SelectionDAGInfo.h
@@ -15,6 +15,7 @@
 #define LLVM_LIB_TARGET_X86_X86SELECTIONDAGINFO_H
 
 #include "llvm/CodeGen/SelectionDAGTargetInfo.h"
+#include "llvm/MC/MCRegisterInfo.h"
 
 namespace llvm {