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!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300336 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed