Add missing #include for STLExtras

Looks like earlier I was relying on #include ordering in files that
used ScalarEvolutionNormalization.h.

Found thanks to the selfhost modules buildbot!

llvm-svn: 300336

llvm/include/llvm/Analysis/ScalarEvolutionNormalization.h

@@ -37,6 +37,7 @@
 #define LLVM_ANALYSIS_SCALAREVOLUTIONNORMALIZATION_H
 
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/STLExtras.h"
 
 namespace llvm {