[MC] Add a missing <memory> include left out of r315327.

llvm-svn: 315331
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.h b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.h
index 960a576..99fec6c 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.h
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.h
@@ -19,6 +19,7 @@
 
 #include "llvm/Support/MathExtras.h"
 #include <cstdint>
+#include <memory>
 
 namespace llvm {